The development of physical influx in early eighteenth-century Germany: Gottsched, Knutzen, and Crusius.

Watkins, Eric

Standard histories of modern philosophy(1) tend to view causality in the following way: After Descartes distinguishes between the mind and the body as two radically different kinds of substance, it becomes problematic as to how such substances could act on each other. Thus, Malebranche develops Occasionalism, which solves the problem by denying that any finite substance has any causal efficacy whatsoever, and Leibniz, dissatisfied with what he sees to be the perpetual miracles involved in the Occasionalist solution, develops Pre-established Harmony, according to which a substance can act, but only on itself. Hume, by inheriting an empiricist account of meaning, is then seen to criticize the very notion of causality insofar as it requires a necessary connection between cause and effect. Such histories typically end with Kant, who attempts to show the incoherence of Hume's critique in his Second Analogy of Experience. There are numerous difficulties with this picture. One is that Kant's contributions to the issue of causality are not exhausted by his reply to Hume in the Second Analogy, since Kant reacts to Leibniz in the Third Analogy as well as in other passages.(2) Another, related difficulty is;that on this picture Leibniz's Pre-established Harmony seems to have no effect on the rest of modern philosophy. This is simply wrong, and what makes it wrong is a philosophically interesting story, namely the development in early eighteenth-century Germany of a view Leibniz opposes to Pre-established Harmony and occasionalism and dubs "influxus physicus" or "Physical Influx."(3)

Before the story can be told, however, some stage-setting is necessary. First, it is important to be clear about the most basic doctrines of Pre-established Harmony, Occasionalism, and Physical Influx.(4) Physical Influx asserts intersubstantial causation amongst finite substances.(5) For instance, when I appear to kick a ball, I really am the cause of the ball's motion. Pre-established Harmony denies intersubstantial causation, but affirms intrasubstantial causation. According to Pre-established Harmony, then, I am not the cause of the ball's motion, but rather the ball is simply causing itself to move (through the unfolding of its complete concept, in Leibniz's version). Occasionalism, like Pre-established Harmony, denies intersubstantial causation, but, unlike Pre-established Harmony, it denies intrasubstantial causation as well. Occasionalism typically asserts that God alone, that is, an infinite substance, is the cause of all changes, and thus of the ball's motion. Though there are other ways of defining these causal theories, this way has the advantage that the causal theories form an exhaustive disjunction.(6)

Second, since I shall be focusing primarily on Pre-established Harmony and Physical Influx, it is worth considering Leibniz's reasons for rejecting Physical Influx and supporting Pre-established Harmony. Leibniz presents two main objections to Physical Influx. First, he repeatedly objects that physical influx is inconceivable because it is incomprehensible how one substance could act on another substance, that is, that an accident from one substance could be transferred or migrate to another substance.(7) Second, he argues that Physical Influx implies a violation of the laws of nature, more specifically, the law of conservation of motion. The idea is that if the mind were to act on the body so as to cause motion, then there would be more motion in the world after the mind's action on the body than beforehand, which is a clear violation of the law of the conservation of motion.(8) Leibniz develops a number of arguments for Pre-established Harmony. For example, in A New System of Nature he claims that Pre-established Harmony is at least possible, since God clearly has the power to endow a substance with an internal force that brings about all its later states. Moreover, it is also the most probable hypothesis because (1) Occasionalism requires perpetual miracles and Physical Influx encounters the aforementioned difficulties and (2) Pre-established Harmony has numerous advantages (for example, it displays our freedom, and the immortality of the soul and it allegedly provides a new proof for the existence of God).(9) I take it that his main positive argument, however, is that a substance (which is defined as something independent of other finite beings and self-sufficient, that is, something that has, to use Leibniz's own term, a complete concept) has no need for the causal activity of other substances.(10) Any causation from without would necessarily be overdetermination (something for which Leibniz has no sympathy). Leibniz may also think that a real relation between substances (as a causal relation would be) is impossible due to the essential reducibility of relations to monadic properties.(11) Thus, Leibniz presents important arguments in favor of Pre-established Harmony.

Third, the intellectual-political situation in Germany in the first part of the eighteenth century requires brief characterization. Intellectually, there are two main camps: on the one hand, the Pietists, led by August Hermann Francke, Philipp Jakob Spener, and Joachim Lange, and, on the other, the Aufklarer, that is, proponents of the Enlightenment, whose intellectual leader is Christian Wolff. Accordingly, when Wolff publishes his major treatise on metaphysics in 1719-20 (significantly, in German), entitled Vernunfftige Gedancken von Gott, der Welt und der Seele des Menschen, auch allen Dingen uberhaupt, (a work now commonly referred to as simply the German Metaphysics), the Pietists finally have in their hands the material they need in order to launch a full-scale attack on Wolff. Despite the fact that Wolff is very cautious in his acceptance of Pre-established Harmony (ultimately he affirms it in its unrestricted form only for the mind-body relationship, not for body-body relationships), this odd and perhaps even dangerous-sounding doctrine is sufficient for Lange and several of his followers(12) to begin their assault because it seems to them to result in determinism, fatalism, and Spinozism. To make a long story short, Wolff wins the battle philosophically, in part because Lange and his followers are not particularly philosophically acute. However, at least in the short run, the Pietists win the battle politically. For during a series of exchanges between Wolff and his Pietist opponents, the Pietists resort to political means to ensure victory, namely, so the story goes, by intimating to King Frederick William I that, according to Pre-established Harmony, a soldier who deserted from the army could not be held responsible for his action because it was already determined beforehand that he had to do it. Frederick William I is naturally not at all disposed to tolerate such a dangerous doctrine and thus on November 8, 1723 gives Wolff 24 hours to leave Prussia or be executed. (Wolff's German Metaphysics is also prohibited from being taught at Prussian universities.) Wolff naturally favors expulsion and leaves for Marburg, where he had previously been offered a chair.(13) (I should note that the Pietists' victory is relatively short-lived, since already in 1740 Wolff returns to Halle upon Frederick II's repeated invitation. In fact, Frederick II even attempts to bring Wolff to Berlin to be codirector of the Prussian Academy of Sciences along with Maupertuis, but Wolff, now suspicious of royal whims as well as of the anti-Wolffian bent of the Academy, politely declines. Also, one can imagine how banishment might make one popular amongst intellectuals of the day. Thus, in part due to the political situation and in part due to his greater philosophical ability, Wolff quickly gains a large following, including figures such as Thummig, Bilfinger, Reusch, Baumeister, Baumgarten, Meier, and Hollmann,(14) to name but a few.) At any rate, the effect of these intellectual-political events is that both Wolffians and Pietists, that is, both camps, give serious philosophical consideration to what is at least prima facie the source of the debate, namely Pre-established Harmony, Occasionalism, and Physical Influx.(15)

Although this stage-setting raises a number of important issues,(16) I shall focus on just one: the development of a version of Physical Influx that is responsive to Leibniz's criticisms and that even has plausible arguments in its favor. What we shall find is that a relatively sophisticated version of Physical Influx emerges from 1732 to 1745 in the writings of Johann Christoph Gottsched, Martin Knutzen, and August Friedrich Crusius. Further, it is interesting to note that two of the three figures who are instrumental in developing Physical Influx, namely Gottsched and Knutzen, are Wolffians, not Pietists.(17)

I

Gottsched's Version of Physical Influx. Gottsched is perhaps best known at present for his literary efforts, since he is often considered to be the first major literary figure of the German Enlightenment. Yet Gottsched is offered and accepts a chair in metaphysics on the basis of his dissertations in philosophy, entitled Vindiciarum systematis influxus physici (1727-29)(18) and his Erste Grunde der gesammten Weltweisheit (1733-34), which is a shortened rendition of Wolff's philosophical system that contributed significantly to Wolff's popularization. However, in both of these works Gottsched parts ways with Wolff on the issue of Pre-established Harmony.

The Vindiciarum systematic influxus physic) divides into two parts. The first part contains primarily an historical account of the three causal theories. The second part, however, contains an extended defense of Physical Influx against the objections primarily of the Cartesians.(19) In particular, Gottsched considers the following objections. First, a Cartesian might object to Physical Influx on the grounds that one cannot clearly and distinctly perceive how the soul and body could act on each other, since their natures are radically distinct.(20) Gottsched responds to this objection by noting that we have insufficient accounts of what it means for the soul to think and the body to be extended. Even if it is clear that thought and extension are the essences of the soul and the body, it does not follow that all of the soul's and body's properties can be derived from their essences. Therefore, the objection that physical influx cannot be derived from the natures of the soul and the body loses its force. Gottsched's response can also be used to provide a preliminary reply to Leibniz's objection concerning the inconceivability of Physical Influx; since we do not have an adequate account of the soul and the body, the lack of a complete description of physical influx is not objectionable, but rather to be expected.

Gottsched then considers the objection that Physical Influx violates the law of the conservation of motion. Gottsched first notes that the law of motion that Descartes and the Cartesians think Physical Influx violates, namely, the law of conservation of motion, has been shown (by Leibniz) to be false.(21) What is conserved is not motion, but, as Leibniz argues, living or motive forces, which are measured by the mass of the body times the square of its velocity. Thus the incompatibility of Physical Influx with a false law is no evidence against Physical Influx. Gottsched then considers whether Physical Influx violates this "corrected" law of nature. In justifying his negative answer, he uses an example of a taut bow. The tension in the string when it is drawn back by an arrow held in one position so that it is at rest contains, Gottsched claims, the same amount of motive forces as does the motion of the arrow when it is released, despite the fact that the amount of motion in the world is clearly not the same in the two cases. Thus, Gottsched can argue by analogy that according to Physical Influx the soul can add motion to the universe or the motion of a body can cause an idea in the soul (possibly diminishing the amount of motion in the universe) without violating the `corrected' law of conservation. The important requirement is that the motive forces of the body and the soul remain constant regardless of whether or not they are impeded by external actions, that is, whether they result in "new" motions. Given that it is not obvious that Physical Influx violates this requirement, this objection to Physical Influx loses its force. In this way Gottsched develops an interesting reply to one of the two main objections raised against Physical Influx. Moreover, Gottsched manages to do so on the basis of Leibnizian principles, since crucial to this response is his acceptance of Leibniz's principle of the conservation of motive forces rather than motion.

Still, in his dissertation, Gottsched's defense of Physical Influx is nothing more than a defense; his main goal is merely to defend Physical Influx from some of the objections that were or might be raised against it. He does not develop any positive reasons for accepting Physical Influx rather than Pre-established Harmony. Gottsched does, however, develop his version of Physical Influx further in his Erste Grunde der gesammten Weltweisheit. In Wolff's philosophical system, which Gottsched's Weltweisheit follows in many respects, Pre-established Harmony arises primarily in two contexts, namely in the Cosmology, which discusses the concept of world, and in the Psychology, which discusses the mind-body relationship. In the Weltweisheit Gottsched maintains what is perhaps best described as an officially neutral position with respect to the general cosmological issue. However, in his discussion of mind-body interaction in the section on Psychology he suggests what may best be described as an unofficial acceptance of Physical Influx.(22) First, Gottsched describes Physical Influx, Pre-established Harmony, and Occasionalism, giving a brief history of each position's advocates and their motivations. He then notes that "none of the three is completely explained or demonstrated; each one of them still has its difficulties: Thus, each person can maintain whichever one is most pleasing. However, for me it has always seemed that: one does not have reason to reject the oldest and most common opinion of natural influence until one has completely refuted it and demonstrated its impossibility. At this point this has been done by no one,"(23) Thus in the Weltweishett Gottsched commits himself in an unofficial way to Physical Influx for mind-body interaction.

His defense of Physical Influx in this domain is limited primarily to responding to some of the objections raised against it (although, as we shall see shortly, he also presents incomplete arguments for Physical Influx). First, in response to Leibniz's and Wolff's objection that physical influx is incomprehensible, Gottsched now explicitly notes that although physical influx may appear incomprehensible to one with obscure and incomplete notions of the body and the soul, it is possible that more distinct and complete notions of body and soul could (in the future) render physical influx intelligible.(24) However, Gottsched also notes ([sections]1067) that "tire word influence [EinfluB] is taken in a metaphorical or `verblumtem' sense."(25) Accordingly, Gottsched further undercuts Leibniz's and Wolff's first main objection to Physical Influx by noting that `influence' (influere) is not to be taken literally as a flowing (of, for example, a liquid), but rather in terms of the capacity or power of a substance to act directly on another substance. Thus, despite his more modest claim that physical influx may be made more comprehensible in the future, Gottsched has already taken an important step toward a more sophisticated and coherent version of Physical Influx.

Second, Gottsched responds to the objection that Physical Influx would destroy the soul's simplicity. On Gottsched's account the soul possesses both the power to represent and the power to move bodies. The objection to this account must be that two such powers would be incompatible with the soul's simplicity. However, Gottsched notes at [sections]1080 that the soul can both will and understand without thereby destroying the soul's simplicity. Even the most orthodox Wolffians claim to derive (apparently without inconsistency) the powers of the understanding and the will from the single representing force of the soul (qua simple substance). Thus, Gottsched argues, Physical Influx does not cause difficulty for the soul's simplicity.(26)

In the second part of [sections]1080, Gottsched proceeds to offer a tentative argument for Physical Influx between the soul and the body. He notes: "the soul has an effort (Bemahung) to bring forth new sensations ([sections]1051). It cannot have this if its body does not have a position and place in the world of the kind that materialists presume can be awakened in the brain through the sensible parts (GliedmaBen). Thus, it strives at the same time according to this changed position or place of the body."(27) Despite its obscure form, Gottsched's argument in this passage is that only physical influx between the soul and the body can render intelligible the soul's desire to bring forth new sensations. For, it is assumed, sensations require a body with a particular place and position in the world. This argument is of course question-begging, since it simply assumes without argument that sensations require the action of a body on the soul, an assumption a proponent of Pre-established Harmony need not make. None the less, Gottsched can still be seen as at least asking the proponents of Pre-established Harmony to explain how a person is to undergo sensations without the causal efficacy of a body.

Since most of Gottsched's discussion in this chapter of the Weltweisheit centers on the interaction between the soul and the body, his unofficial acceptance of Physical Influx might seem to be limited to the soul-body relationship. However, in [sections]1081 Gottsched commits himself in a limited and equally unofficial way to Physical Influx with respect to the general cosmological issue as well. That is, Gottsched seems to admit that substances can act on each other, regardless of their particular natures. He argues that we need not say that the soul taken by itself possesses the entire power of moving a body. For "there are so many powers already in the fluid parts of the body: that these powers require only stimulation and determination if they are to act. Though we cannot explain how it is that the soul brings some nerve fluid (Nervensaft) into motion; so too with respect to bodies we cannot completely comprehend how one ball hitting another can set the other in motion. For since monads or elements are present in all points at which they are in contact: these [monads or elements] must be able to act on each other and continue the motion, even if we do not know how."(28) In other words, Gottsched seems to be arguing that physical influx between the soul and the body implies physical influx among bodies.(29) For the soul is not sufficient to move all of the body's fluid parts, but rather these fluid parts must be able to move each other. Moreover, he wants to suggest that just as we do not completely understand physical influx between the soul and the body, we do not completely understand physical influx between bodies, so no objection can be raised against Physical Influx on that count. Thus, for Gottsched, Physical Influx at the cosmological level has the same (unofficial) status as it does for the soul and the body.

Finally, Gottsched adds a brief argument in the final section of this chapter ([sections]1082) against Pre-established Harmony. He asks rhetorically: "But could the soul have all its sensations even without it [the body]: For what use would the body be? An idealist would then have a much better opinion; because by rejecting bodies he would have transcended innumerable difficulties."(30) Gottsched's criticism is that if a soul could have all of its sensations without a body, then the body would be superfluous and idealism would represent the most attractive position.(31) Nonetheless, these two arguments are quite brief and directly after this last argument Gottsched adds: "Yet I present all this only as mere speculation and do not decide which opinion, with a more mature knowledge of the soul and the body, will gain the upper hand with time."(32) However, in later editions of this work, immediately after making this conciliatory remark, Gottsched refers the reader to his dissertation on the topic, making it clear that he has a definite opinion! Thus it seems appropriate to interpret Gottsched's statements (especially about the cosmological issue) as unofficial or personal remarks about his own opinion rather than a philosophical claim that can stand on the basis of the arguments he presents.

Gottsched's contribution to the debate about Pre-established Harmony and Physical Influx is thus quite substantial, even if not definitive. For although he does not take an official stand on the issue, he is unequivocal about the possibility of Physical Influx, since he responds to a number of important objections raised against that theory. Also, he provides reasons, even if not compelling ones, for accepting his unofficial version of Physical Influx. Perhaps his most important achievement, however, is to suggest that physical influx should be taken, not in a literal but rather in a metaphorical sense, according to which physical influx is not an inconceivable migration of accidents, as Leibniz and Wolff charge, but rather the capacity or power a substance has to act directly upon another substance.

II

Knutzen's Version of Physical Influx. The second major advocate of Physical Influx--who forms the crucial turning point in the debate--is Martin Knutzen. Knutzen is now best known (and this is faint praise, since he is not at all well-known) as one of Kant's teachers in Konigsberg. However, in the first half of the eighteenth century he is well-respected in academic circles for his writings in philosophy, theology, natural science, and mathematics; some of his writings are De immaterialitate animi (1741), Philosophischer Beweis von der Wahrheit der Christlichen Religion (1740), Vernunftige Gedanken von den Cometen (1744), and Theoremata nova de parabolic infinitis eodem parametro et circa eundem axin descriptis (1737).(33) However, his real claim to fame is his dissertation, which he publishes in 1735 as an independent monograph, entitled Systema Causarum efficientium, of which a second edition is issued in 1745. What should be emphasized, however, before we consider the details of this treatise, is that in the course of its three parts, 62 sections, and 210 pages, Knutzen is explicitly and forcefully arguing for Physical Influx as an "official" position rather than merely hinting at privately held beliefs or timidly claiming that Physical Influx is perhaps still possible, since no other theory has been definitively proven.

Further, what makes Knutzen's argument so influential is that it is based on Leibnizian principles. Despite the fact that there is considerable difficulty in determining which of Leibniz's works Knutzen would know, Knutzen himself refers to Leibniz's letters to Wagner, "A Brief Demonstration of a Notable Error of Descartes and Others concerning a Natural Law," A New System of Nature, and the Theodicy; and additionally the Monadology and On Nature Itself had been published before 1735,(34) so that it is safe to conclude that Knutzen has access to many (if not all) of Leibniz's fundamental philosophical doctrines. Moreover, Knutzen often supplements his references to Leibniz with references to Wolff, who, despite his departure from Leibniz on certain points,(35) is clearly still a Leibnizian. Thus we have sufficient prima facie evidence to take seriously Knutzen's claim to be basing his argument on Leibnizian principles, with one major exception, namely, Leibniz's complete concept theory of substance.(36) There is simply little trace of that doctrine to be found in Knutzen's account of Leibniz, and insofar as Leibniz bases Pre-established Harmony on this doctrine, Knutzen misses part of Leibniz's motivation on this point. However, it is also possible that Knutzen is aware of this doctrine, but simply finds it unreasonably strong and thus worthy of being rejected tout court. At any rate, Knutzen does not misunderstand the main points of Leibniz's position even if he is unaware of or rejects some of the more unusual details of Leibniz's conception of substance. With this in mind, let us now turn to Knutzen's treatise.

The first part gives a general introduction to the topic, explaining the empirical correlation that holds between the states of the mind and the states of the body, stating precise definitions of the three causal theories, and arguing that direct experience cannot decide the issue between them. It is worth noting that Knutzen's argument that direct experience does not decide the issue is not novel. During the debate between Wolff and various Pietists, Wolff repeatedly argues that all three causal theories are consistent with what we directly experience. Thus all parties to the dispute agree that the issue must be decided by argument, not observation.

The Argument from vis motrix. In the second part Knutzen presents four distinct arguments for Physical Influx. In order to lay the necessary foundation, he first carefully articulates definitions of the following: human beings ([sections]17), spirit or monad ([sections]18), bodies or composites ([sections]19), action ([sections]21), force ([sections]22), space, place, and position ([sections]23), internal and total motion, and motive, primitive, and derivative forces ([sections]243. Accordingly, Knutzen interprets Leibniz's position to be roughly that of the New System of Nature,(37) namely, that there are simple elements or substances that compose bodies(38) and that are in a place, though they do not fill a space.(39) He then proposes his first, and what amounts to his most important argument for Physical Influx in [sections]28:

[sections]. XXVIII. A force [of something] to move itself involves in

reality a force of moving another as well.

A force of moving that brings it about that any being changes its own

proper place without the force of moving other things that surround it

cannot be conceived, but rather it is necessary that after positing one the

other is given at the same time. For a force of moving that brings it about

that a being changes its own place does not exist except as a conatus for

changing its own place ([sections]. 24.) that is, for occupying a place

distinct from the one that it now occupies, yet one that is still continuous

to it ([sections]. cit.). But other coexistent things that surround the

movable thing on all sides hold a place distinct from the place of the

movable thing, since two distinct beings cannot be in one place at the same

time ([sections]. 23.): therefore, a being endowed with the force of moving

itself strives to push things to another place, if they resist. But if in

truth they are also supposed to yield spontaneously, nevertheless,

that which is already participating in progressive motion exerts itself in

the way which is required to complete the motion

beyond itself or to push things to another place. Because resistance is

to such a degree the occasional cause of motion, it does not add

anything to the intrinsic force: Therefore, a being that moves itself enjoys

the effort of changing the place of coexistents or the force of moving

other things ([sections]. 24.). Therefore, the force of moving itself

without the force of moving other things cannot be conceived, but after the

one has been posited, the other is posited at the same time.(40)

This is an interesting argument. The basic idea is that if, as Leibniz and Wolff assume, a being possesses the force to change its place,(41) and the change of place of one being implies the change of place of another being,(42) then the force to change its own place implies, now contra Leibniz and Wolff, the force to change the place of another being. More abstractly formulated: Intrasubstantial causation implies intersubstantial causation. This argument can be formulated in two different versions. The first version would claim that insofar as one being moves itself it in fact causes the motion of the other. The second version, which I shall discuss shortly, would claim that the mere capacity of a being to move itself implies that it could move the other, which is enough to contradict Pre-established Harmony as Leibniz defends it.

What might Leibniz find objectionable in the first version of this argument? What is unquestionably right in the argument is that the fact that one being changes its place implies that another being must change its place too (if it occupies the place into which the first being is to move). Leibniz will presumably argue, however, that it is illegitimate to infer from this fact that the motion of the second being must be caused by the first being, since according to Pre-established Harmony each being will be causally responsible for its own changes. Thus, the fact that the first being has the force to move itself implies only that either the first or the second being has the force to move the second being. In other words, all that the motion of the first being implies is that there be some cause of the motion of the second being. On what grounds does Knutzen infer that the cause must be located in the first being?(43)

Knutzen has, I believe, resources to answer this question. Even if one grants Leibniz that the second being has the force to move itself, Knutzen can argue that what activates the force in the second being must be precisely the force of the first being. In other words, even if Knutzen admits causal activity in the second being, he need not accept that this causal activity is sufficient for the second being's motion. After all, if the first being had not moved itself into the place of the second being, the second being would not have moved itself either. Thus it seems entirely appropriate to say that the first being has the force to move the second being even if it does so only in virtue of acting on the latter's force.(44) Leibniz holds that what is responsible for the motion of the first being is merely an ideal ground of the second being's motion.(45) However, from the perspective of a proponent of physical influx it is difficult to see why such a ground is ideal and not real, that is, causal.

Leibniz might reply to Knutzen's explanation with his "world apart" doctrine,(46) which states that the appearances would (or could) be entirely the same as they are even if nothing other than God and I existed (as, so to speak, a world apart), and the plausibility of this doctrine might appear to be evidence in favor of the sufficiency of internal causes. Despite the fact that there is no evidence showing that Knutzen accepts the "world apart" doctrine, Knutzen can grant this doctrine and still claim that internal causes are not sufficient. How? The "world apart" doctrine states that if only God and one being (namely I) existed, the appearances would be no different from what they are now. However, such a claim is in fact irrelevant to what Knutzen is arguing. For Knutzen is concerned with the relationship that exists between what in fact exists. Surely a different relationship would hold in the counterfactual situation in which only God and one being existed.(47) Thus, applying the "world apart" doctrine to our second being, to say that what is contained in the complete concept of the second being would be sufficient for its own motions if nothing else existed is not to say that what is contained in the complete concept of this being is sufficient for its own motions, given that other beings do in fact exist. For unless Leibniz and Wolff are to beg the question, the presence of other beings could be causally relevant. And this is precisely what Knutzen is claiming to be the case. Why? Because he is claiming that the motion of one being necessarily implies the motion of another. That is, the force a being has of moving itself implies the force to move another being. Thus, since it is not logically possible that the second being could not move, given the motion of the first being, it seems that there is a sufficiently strong relationship between the first and second beings that Knutzen is justified in calling the first the (or at least a) cause of the motion of the second.

Knutzen need not, however, rely only on common sense or standard linguistic agreement here. Consider a Leibnizian definition of action. In [sections]21 Knutzen states: "A being is said to he acting when it contains in itself the reason for the existence (or change) of a certain thing."(48) If this definition is accepted, then it seems correct to infer, as Knutzen does in this first main argument, that the force of one being to move itself does imply the force to move another, since the change of the one does contain in itself the reason (or at least part of the reason) for the other's motion. Could a Leibnizian simply reject this definition of action? Not easily, since it would seem that any narrower characterization might simply beg the question. For if action is simply defined in such a way that a being can act only on itself, then such a definition obviously involves a petitio principii.

Now a Leibnizian might object to this kind of response in the following way: If one accepts the account of causal action developed above, then, due to the expression thesis(49) (namely that every substance expresses or mirrors the entire universe), one would be committed to saying that every substance would cause every change in every other substance, which is rather implausible. Of course one might accept the above account of causal action and take this argument as grounds for rejecting the expression thesis. However, Knutzen could accept the expression thesis and still make a distinction amongst grounds in such a way that any being will not cause all changes in all other beings. How? The difference between a case in which one being moves so as to displace another being and a case in which one being simply moves, say, closer to the other without moving it is that in the former case there must be some intrinsic change in the being that is displaced, whereas in the latter case there need be no such intrinsic change, since the change that occurs is merely relational and can be attributed wholly to the first being, which cannot be done in the first case.(50) In other words, one can distinguish between grounds that require an intrinsic change in a distinct being and those that do not. Only the former, Knutzen can suggest, are really causally active on distinct beings.

Let us now briefly turn to the second version of Knutzen's argument, a version considerably weaker and less controversial, but still sufficiently strong to present difficulties for a Leibnizian. If a being has the force to move itself, then, even if the being contiguous to it moves of its own accord, the first being must nonetheless have the force to move it, in case it had not moved of its own accord. If the first being had the force to move itself only if the second being moved itself of its own accord, then it is not appropriate to say that the first being really has the force to move itself, since it does not contain the sufficient conditions for its motion in itself (which is the standard condition Leibniz would set for the ascription of a causal power). In other words, it must at least be possible that the first being move the second, even if God sets the world up in such a way that this force need never be exercised. However, if it is possible that the first being move the second, then Knutzen can conclude that Pre-established Harmony is false insofar as it implies that intersubstantial causation is not even possible (on the grounds that it is not even conceivable). Thus, even this second, weaker version of Knutzen's argument can be presented against Pre-established Harmony.

The Argument from Impenetrability. In [sections]29 Knutzen provides a second argument for Physical Influx, which, though distinct from the first argument, clearly stems from similar considerations. He writes:

The same can also be demonstrated another way: simple elements are

impenetrable, according to the opinion of the illustrious Leibniz, who

asserts that all finite substances are impenetrable. See his Letter to C1.

Wagner p. 201. Tom. I. Epist. Edit. Kortholtianae. Hence, it cannot be the

case that one [substance] is in the place of another. Therefore, there is

something real, by whose force one simple excludes and pushes up

against another, lest the other invade its place. For since it is most

certain that simples are moved ([sections]. 27) and that distinct simples are

not moved according to an opposite line of direction, consequently it is

impossible that they penetrate each other mutually, or rather what we

may gather from the conflict of bodies and their collision is that in fact

they are carried in a contrary direction mutually away from each other;

It follows in this case that one must hold that either simples penetrate

each other mutually, which goes against Leibniz's assertions, or if they

resist each other mutually, they must act on each other mutually.

Q.e.d.(51)

As in the first argument, Knutzen tries to show that some property that a Leibnizian will want to ascribe to finite substances implies intersubstantial causation. The basic idea in this argument is that impenetrability is intelligible only if one substance is attempting to penetrate a second substance, whereby the second substance is said to be impenetrable in virtue of resisting the first substance. But, the argument continues, how can one substance be said to resist another substance if not causally? That is, surely resistance is a causal term, and a substance cannot resist itself, so that if resistance (or impenetrability) is a real property of substances, then there must be interaction between substances. In the case of impenetrability and resistance, even more than in the case of the motion of one being implying the motion of another, natural linguistic usage suggests causal interaction amongst substances.(52)

Leibniz's most plausible response to this kind of argument is to argue that one should divorce such causal connotations from the concept of resistance. According to Leibniz, resistance must be, properly speaking, simply a fact about substances, namely that substances cannot be in the same place. However, Knutzen seems justified in pressing Leibniz on this point, since the fact that substances cannot be in the same place seems quite distinct from the issue whether substances are impenetrable and can resist each other. (One would naturally think that resistance is the means for keeping substances from occupying the same place.) To put the problem with Leibniz's response in words closer to his own, Pre-established Harmony seems to arrange the motions of bodies with such great harmony that they have no need to resist each other in the first place! Thus, ultimately, Knutzen's second argument forces a Leibnizian either to accept Physical Influx or to reject impenetrability and resistance as real properties.(53) I suspect that if Leibniz were faced with this choice, he would retain Pre-established Harmony and cast resistance aside, albeit reluctantly, since then it would follow that two substances could be in the same place at the same time (even if they never in fact are so).

The Argument from the Simplicity of (Divine) Action on Others. These first two arguments are quite general; the first holds for any being that can move itself and the second for impenetrable simple elements or substances. In [subsections]30-2 Knutzen makes preparations to extend the scope of Physical Influx from beings per se or "simple elements" to the mind-body relationship by explaining what perception is ([sections]30) and by arguing that simple elements perceive ([sections]31).(54) However, in [subsections]33-34, instead of simply applying to the mind in a straightforward way the arguments that he has already constructed for simplex, Knutzen introduces a third argument for Physical Influx, an argument that takes a rather interesting turn. For in [sections]33 Knutzen considers the nature of absolute perfection. "Perfection that implies no limitation per se or, alternately, that can exist together with any other possible entity (as the Scholastics say) is called perfection absolutely or simpliciter. However, it is demonstrated in natural theology that anything truly ascribed to God is a perfection simpliciter, which does not contradict anything, except limitations or imperfections."(55) In [sections]34 Knutzen then uses this conception of perfection to establish that physical influx is possible for the mind-body relationship, since it involves no contradiction. His justification is as follows:

The physical influx of the mind on corporeal simples and of those simples

in turn on the mind is completed by an act ([sections]32). Therefore, if

one must demonstrate that physical influx is possible, then one must show in

what way the action of the mind outside itself on other simples does not

involve a contradiction ([sections]. 85. ontol.): Therefore, let's

investigate especially

whether one can discover anything in the mind that contradicts the mind's

actions on external things. We discover in the mind those things that

primarily

amount to this: that the mind is a simple being and surely that this being

perceives or is a perceiver, and in a far greater degree of eminence than

that of

simple elements, since it perceives distinctly or is provided with an

intellect or

a will [sections]. 17. 18). The action of the mind on external things

cannot contradict

[the] simplicity [of the mind] because not only does God act outside himself

(according to the Princ. of Nat. Theol.), but also the simple elements act on

each other mutually ([sections]. 29.). Nor can this action contradict the

mind to the

extent that it is a being that perceives or is perceiving because simple

elements take pleasure in the perception of external things ([sections].

31); however,

an action of this kind cannot be denied to these simples. Therefore, nothing

remains other than that eminent perfection by which the human mind is

separated from simples that have inferior perceptions, and that places the

faculties of understanding and willing in the mind, and if the external

action of

the mind does not contradict this, then the possibility of physical influx

will

have been established beyond doubt. But action on external things is a simple

perfection because it can be ascribed to God ([sections]. 33); and

therefore it cannot

be inconsistent except with limitation and imperfection ([sections]. cit.):

therefore, it

cannot be inconsistent with intellect and volition, which exceed the mere

faculty of perception, and which at the same time confer a greater perfection

on the being, since, as was already shown, this kind of action is agreeable

with a merely perceptive being and a more perfect being. Therefore, who could

doubt that the mind can act on the body? However, because it was

demonstrated above ([sections]. 29.) that action on other simples must be

attributed

to the simples of which the body consists; surely the mind, insofar as it is a

simple substance, can act on such simples (according to the demonstr.): there

will be no reason why anyone should judge the action of the body's simples

on the mind to be impossible. Therefore, it is established that physical

influx is possible.(56) Knutzen's main argument in this passage is that since we know that it is possible for less perfect simples to act on each other, it is legitimate to infer that it is possible for more perfect simplex, that is, for substances endowed with intellect and will, as minds are, to act on other simples. Indeed, this is precisely the argument we expect. However, Knutzen supplements this argument with the idea that physical influx is possible for minds because God has the perfection of acting in this way, presumably in creation and in miracles. In other words; what is interesting is that Knutzen characterizes acting on others (that is, physical influx) as a perfection and what allows him to do so is the fact that God has this perfection in creation. This characterization strengthens his argument because the mere fact that the substances or simple elements that constitute bodies can act on each other does not imply that other kinds of substances or simple elements can act on bodies, even if the latter are more perfect than the former. However, given that acting on others is a perfection (and it undoubtedly is, if God does it), it is more plausible that if a lesser being can do it, so can a greater being (especially if the differences between the two are differences of degree rather than of kind).(57)

Another important factor involved in the argument concerns simplicity. Not only is acting on others apparently a perfection, but it is also absolutely simple. This is relevant in two ways. First, that such an action is simple is the crucial feature in showing that it cannot result in a contradiction. In criticizing Descartes' ontological argument, Leibniz often remarks that the argument shows only that if God is possible, then He necessarily exists. What Descartes still needs to show is that God is possible. Sometimes Leibniz leaves the reader wondering whether such an argument can be developed, but occasionally Leibniz does suggest that such an argument can be given by considering that all of God's perfections are simple and simples cannot contradict each other.(58) Thus the fact that acting on other substances is simple is important for showing that there is no contradiction in asserting that the mind can act on the body. Second, it brings out a feature of Knutzen's version of Physical Influx that was only implicit in the previous discussion, namely that the force of acting on others is primitive or basic; that is, it cannot be explained in more basic terms. In other words, Knutzen is at least implicitly arguing that one cannot go any deeper than to say that a substance has the capacity, force, or power to act on another substance. Any suggestion that such an action must be explained further in terms of accidents migrating from one substance to another (as Leibniz likes to do, perhaps unfairly, on behalf of the proponent of Physical Influx) is illegitimate.

What is of further significance is that a Leibnizian cannot object to such a primitive force of action because Leibniz himself assumes such a force insofar as it is through a conatus or force that a substance strives to change from one state to the next! In other words, by accepting intrasubstantial causation Leibniz must be accepting some kind of capacity for a substance to act on itself. So the very idea of such an action cannot be objectionable. The difference between Leibniz's and Knutzen's force is of course that Leibniz's force acts on itself, whereas Knutzen's force acts on other substances. But why should this difference be important? The insight underlying Leibniz's suggestion that one substance can act on another only if an accident were to migrate from the one substance to the other is presumably that a property cannot pop into existence but rather must come from some source (namely from the substance that is acting). If it comes from the substance that is acting, then it must somehow get from the one substance to the other and how could it do that if it did not migrate there?

Knutzen has a number of responses to this point. First, this objection still does not clarify what the special difficulty is with one substance acting on another substance as compared to a substance acting on itself. For if it is legitimate to ask about the source or origin of a property, both accounts face the same dilemma: Either the property is already present in the substance, in which case no force is necessary in order to make it true of the substance. Or it is not already present in the substance, and then creation ex nihilo will be equally problematic for both inter- and intrasubstantial causation, for if creation ex nihilo is solved by the concept of force, then that concept should solve it for both Pre-established Harmony and Physical Influx. Second, even if there is some special (albeit unspecifiable) problem with the "inter" part of intersubstantial causation, Leibniz has not countenanced Knutzen's specific version of Physical Influx, since, as we have seen above, for Knutzen two forces are involved in the production of a property, one in the substance Knutzen wants to call the cause and one in the substance of which the property will be true.(59) It seems open to Knutzen to respond to Leibniz's charge by claiming that the second of the two forces alleviates this problem. Thus Knutzen has cleverly undercut any Leibnizian grounds for objecting to a substance's simple force of acting on others.

The Argument From Probability. Knutzen's final argument for Physical Influx stands one of Leibniz's arguments for Pre-established Harmony on its head. After establishing in [subsections]33-4 that Physical Influx is possible, in [sections]35 he turns to show that it is more probable than the other two causal theories by considering a number of criteria of truth. First, it agrees with experience, a point Wolff admits. Second, as [sections]34 has shown, it is possible. Finally, and perhaps most importantly, Knutzen argues that it agrees with divine wisdom. "For it is shown in natural theology: God, in conformance with his greatest and infinite wisdom, chooses the natural, shortest path."(60) Knutzen proceeds to explain what the shortest path is, namely, that "those things that can come about naturally through a select few will not be completed through many or by the longer path."(61) In the explanatory text to this passage, Knutzen emphasizes that it is not enough that God choose the shortest path, but it must also be a natural path, by which he means one containing the fewest miracles.(62) In the next section ([sections]36) Knutzen then explicitly argues that Pre-established Harmony involves "roundabout ways because so many skills are necessary for producing this harmony both in the body and in the mind, that they may surpass every form of comprehension."(63) In other words, the Harmony in Pre-established Harmony is guaranteed by God's benevolence and wisdom rather than by the natural powers of finite substances alone and thus extends well beyond our understanding, which Knutzen takes to be tantamount to miraculous.(64) Knutzen's point here is well-taken. If we would have to perform infinite analysis in order to understand a simple causal connection between two events, an impossible task, then it appears that Physical Influx, according to which we would need to understand only the causal powers of both substances, is the shorter, preferable, and thus more probable path.

Objections and Replies. In the third part Knutzen states and responds to ten objections to Physical Influx, many of which are raised by perhaps the leading Wolffian defender of Pre-established Harmony, Georg Bernhard Bilfinger(65) in his works De harmonia praestabilita (1723)(66) and Dilucidationes philosophicae de Deo, anima humana, mundo et generalibus rerum affectionibus (1725). While it is not possible to consider all of these objections in this context, it is worth discussing three of them insofar as they elicit Knutzen's reply to the one charge against Physical Influx that has not yet been given due consideration: that Physical Influx violates the law of the conservation of motive forces.(67) Objection 6 ([sections]53) considers this objection explicitly, while Objections 7 and 8 discuss it implicitly, since they concern the proportion (in [sections]54) and cause-effect relationship (in [sections]55) that are supposed to hold between the motions of the body and the decrees of the mind. Briefly, the difficulty concerning proportionality is that causes and effects must be proportional to one another, but the mind and the body are not homogeneous and thus cannot be proportional.(68) The difficulty concerning the cause-effect relationship is that the effect would be greater than the cause if a certain motion in the body could cause not only another motion but also a thought in the mind, as Physical Influx asserts.(69)

Knutzen's main response to the objection that Physical Influx violates the law of the conservation of motive forces is to deny that the law holds for mind-body interaction. But he does so in two distinct ways. He first notes that the law has been proven only for elastic bodies, not for inelastic bodies, much less for the mind and the body. This is part of what he means when he emphasizes: "I deny .. . that it follows from Physical Influx that a certain quantity of living forces is not conserved in the collision of bodies amongst each other"(70) and "as long as it has not yet been shown and cannot be shown that this law of motion about conserving a certain quantity of living forces is not only dictated for bodies acting on each other mutually, but also for the mind acting on the body and vice versa, there is absolutely no objection present that injures Physical Influx."(71) Indeed Knutzen even provides a reason why this law should not hold for the mind. Since Leibniz derives the conservation of motive forces from the law of inertia ("that any body remains in its state of rest or uniform motion in a direction unless it is forced to change its state by an extrinsic cause") and "it is most evident that the mind does not at all remain in its state of rest and uniform motion in a direction until forced to change its state by an external [cause]"(72) (that is, the law of inertia does not hold for the mind), there is no reason for the conservation law to hold for the mind.

However, in his discussion of the objections concerning proportion and the cause-effect relationship Knutzen considers the relationship between bodies and minds in more detail and then suggests another way in which to respond to the charge that Physical Influx violates the laws of nature. For example, in [sections]55 Knutzen writes:

One must note the following concerning physical influx: 1) that the

impression of motion that is communicated to monads causes perceptions

in them, for the communication of motion cannot be completed

except through the modification of forces that are present in elements

and that Leibniz calls perceptual. And thus beyond the communication

of motion nothing else is required in order to cause perceptions; and as

it is in the case of the monads of the body, so it is in the soul.(73)

In this passage and others,(74) Knutzen can, I think, be understood to be making a more fundamental criticism of Leibniz's objection along the following lines. Naturally, the law of the conservation of motive forces holds for bodies, and at least for the Leibniz of the Monadology bodies pertain to the realm of well-founded phenomena.(75) Thus bodies and their motions are well-founded insofar as a corresponding monadic, that is, representational state, whatever it may be like, underlies them. Further, we know about this founding relationship only that the law of efficient causes holds for the phenomenal realm of bodies (and their motions) and the law of final causes holds for the realm of monads that founds the phenomenal realm. Thus Leibniz is committed to holding that the laws of motive forces will hold for the phenomenal realm, apparently regardless of how the monads exercise their freedom. In other words, no difficulty arises for Leibniz that the activity at the monadic level, however free it might be, could violate the laws that govern the phenomenal level. The crucial point to note in this explanation of how Leibniz avoids the problem presented by freedom is that no mention is made of Pre-established Harmony.(76) In other words, Leibniz's own way of avoiding the problem of reconciling freedom and the law of the conservation of motive forces is to drive a wedge between monads and bodies, claiming that the motions of the latter are somehow grounded in the perceptions of the former, though the laws for each are completely distinct. Accordingly, the laws of motion will presumably be what they are, whether each monad acts only on itself according to final causes of one sort or whether they act on each other according to final causes of another sort. Also, whether this monad causes a motion in the body that results from it (as Pre-established Harmony would have it) or whether it causes a motion in a body that does not result from it (as Physical Influx would allow), is not obviously relevant to whether the law of the conservation of motive forces holds. Thus, contrary to what Leibniz suggests, Pre-established Harmony is not the only solution to this problem.(77) I take it that Knutzen is aware of this when he remarks that the law of the conservation of motive forces holds only for bodies and that the mind's perceptions and free decrees will correspond to the motions in the body, since "in whatever way it is in the monads of the body, it is similar in the soul."

Since this is an important point, let's consider it from a different angle. The objection to Physical Influx is that when the mind causes a body to move, this action adds to the total amount of motion (or motive forces) in the world, that is, motion (or motive forces) is not being conserved. The inference Leibniz wants to draw from this objection is that one should deny that the mind acts on the body. However, one can also infer (and such an inference is suggested by Leibniz's ultimate position) that one should distinguish between the realm of bodies and the realm of minds or monads and claim that the latter founds the former in some general way. Thus when the mind causes a motion (or motive force) in bodies, there is no reason to think that there is more motion (or motive force) afterwards than beforehand because presumably this action is just part of a general founding relationship that exists between the two realms. In other words, the "new" motion (or motive force) would have occurred even if the mind had not chosen to act in the way it did, and the reason the motion could have occurred is that it is simply obeying the laws that hold for its respective realm, laws that, generally speaking, are founded on the monads. So what is crucial to solving the problem posed by the law of the conservation of motive forces is not Preestablished Harmony, but rather restricting the law to bodies (as Knutzen explicitly does), since minds have their own laws (or free decrees) though they correspond to (or found) the bodies. In this way Knutzen can give a philosophically interesting response to Leibniz's second main objection to Physical Influx, namely that it violates the laws of nature.

Summary. Martin Knutzen's treatment of Physical Influx and Pre-established Harmony is of fundamental importance to the debate both historically and philosophically. Knutzen's work surely represents the crucial turning point in 1735 against Pre-established Harmony and in favor of Physical Influx. Whereas previously Wolffians had generally followed Wolff on the issue and Gottsched's unofficial wavering did little to change this, after Knutzen's work it becomes acceptable (even for Wolffians) to adopt Physical Influx. For example, Crusius, Darjes, Ploucquet, and even Euler all accept Physical Influx in the 1740s.(78) And recall what Knutzen has accomplished. He has given four arguments in favor of Physical Influx, at least two of them rather interesting ones, and all of them based on Leibnizian principles. He has responded to two of the most important objections that were lodged against Physical Influx, by noting that the law of the conservation of motion (or motive forces) holds only for bodies and by developing a model of intersubstantial causation. According to this model, physical influx is not literally a migration of accidents, as Leibniz alleges the scholastics to have supposed, but rather the force of one substance to act on another substance. In addition to being distinct from the migration model, this model has the advantage that it appeals to a concept of force that a Leibnizian has no reason to find objectionable, since an analogous force is invoked by Leibniz himself to explain the unfolding of a substance's complete concept. Knutzen also provides a rather sophisticated description of the model, since the powers of both substances must be involved in physical influx insofar as the power of one substance modifies or activates the power of another, which then produces the new property. For example, when the body acts on the mind, a corporeal element is causally efficacious by modifying the substantial representational power of a noncorporeal element in such a way that corresponding new representations are produced out of it. This model allows him to avoid the untoward consequence that, for instance, a body (something material) is sufficient to produce representations (something Knutzen holds to be immaterial), since the noncorporeal element (that is, its representational power) can be responsible for producing the specifically mental dimensions of the representations, even if it is not sufficient for explaining these representations in their entirely.(79) Accordingly, not only does Knutzen explain that substances can act directly on each other, as Gottsched does, but he also provides a more detailed model of how they can do so.

Although Knutzen's development of this sophisticated model of Physical Influx signals the victory of Physical Influx over Pre-established Harmony, I maintain, against Erdmann,(80) that the debate is not yet over. Two issues are still of particular importance to proponents of Physical Influx. First, what is the best way to argue for Physical Influx? This is especially important because Pre-established Harmony would experience something of a revival in the late 1730s and early 1740s with Baumgarten's and Meier's spirited defense. Second, what version of Physical Influx ought one to maintain? For some answers to these questions, we can turn to Christian August Crusius.

III

Crusius's Version of Physical Influx. Crusius develops his version of Physical Influx most clearly in his Entwurf der nothwendigen Vernunft-Wahrheiten in 1745 and in his Weg zur Gewi[beta]heit und Zuverla[beta]keit der menschlichen Erkenntnis in 1747. Let us consider each of these works in turn.

The Entwurf. In his Entwurf der nothwendigen Vernunft-Wahrheiten Crusius first discusses Physical Influx in his section on cosmology. One might think(81) that Crusius presents an argument for Physical Influx from the very definition of the essence of the world.(82) For he defines the world as "a real connection of finite things that is not itself in turn a part of another to which it belongs by means of a real connection."(83) Also, it is natural to think that what Crusius means by the term `real connection' is intersubstantial causation. However, on close reading of Crusius's explanation of this phrase, we can see that Physical Influx is not implied by, even if it is compatible with, this definition. Crusius's intent in adding `real connection' is rather to allow for a distinction between possible worlds. As Crusius puts it, "we distinguish a world from several simultaneously existing creatures or sums thereof that do not stand in any connection. The world is to be a unity (eines) and one that is a unity outside our thoughts as well. Consequently, the things belonging to it must stand in real connection."(84) The justification for calling the connection real is that if the connection were ideal (that is, consisted in our thoughts alone), then there would be only one possible world, since every possible object of thought could be connected ideally (that is, in our thoughts).(85) However, if it were a necessary truth that there is only one world, common linguistic usage would be violated, since we tend to think that there are various different ways the world might have been rather than just one.

If this argument is an adequate reconstruction of Crusius's considerations here, then Physical Influx does not follow from it, or at least not directly. What the definition of the (essence of the) world requires is that we be able to distinguish more than one possible world. This requirement can be met by distinguishing between real and ideal connections. It may be the case that a real connection implies Physical Influx, but then the argument for Physical Influx is located not so much in the definition of the world as in the notion of a real connection. For presumably Pre-established Harmony need not contain an ideal connection in the sense intended by Crusius, but rather what he would call a real connection. Wolff, for example, claims that monads are directed toward all other monads in a single world, but is agnostic about whether or not `directed toward' is to be interpreted as the ideal connection of Leibuiz's `representing'. Thus Wolff's agnosticism about `directed toward' leaves open the possibility of distinguishing possible worlds in terms of a real, albeit noncausal relation. For example, it would suffice for present purposes if God were simply to stipulate what constitutes a given possible world, so that God is responsible for the "real connection".(86) Thus it is not the definition of the world that directly implies Physical Influx,(87) but rather the general notion of real connection.

In an earlier section ([sections]94), Crusius provides just such an argument for Physical Influx. In describing the various possible kinds of connection between things, Crusius notes that

any connection of finite things that is to be a real undo existentialis outside

thought must rest on a causal connection of things due to which at

least one must act on the other, but also both can act on each other

reciprocally as well as be passive with respect to each other. For there

is otherwise nothing else outside thought that can provide a ground of

connection between complete things. But as soon as one takes this

away, then one must connect them only in a concept in the

understanding, that is, the things thus have either no or a merely ideal

connection. Consequently, I cannot, for example, admit that those who

believe in pre-established harmony leave a real connection between

body and soul.... Their connection is only ideal even with respect

to God. One cannot even say that they are connected by the intervention of

God. For then at least the arrangement (Einrichtung) of the essences

(Wesen) of the body and soul would have to be attributed to God. But the

defenders of pre-established harmony can never say this in the Leibuizian

sense because they do not leave God any honor beyond bringing the

essences of substances into existence, rather than arranging them, because

all beings are to be eternal. Thus, a mere correspondence rather than a real

connection remains.(88)

Crusius's main argument(89) is that the ground of a real connection must be a causal connection because nothing other than a causal connection can provide a ground for a real connection. Yet in order not to beg,the question against Pre-established Harmony, Crusius must explain why, for example, God cannot be a sufficient ground of a real (mundane) connection. Crusius argues that proponents of Pre-established Harmony (or at least Leibniz) can ascribe to God's action only a mere correspondence(90) between substances rather than a real connection (and dependence) because although God brings beings into existence, God is not responsible for their essences (since their essences are given necessarily in the Divine understanding and cannot be altered by the Divine will).(91) Thus Crusius is claiming that, according to Pre-established Harmony, although God can bring into existence substances that correspond to each other, God cannot bring substances into existence with a real but noncausal connection. However, Crusius's claim seems both dogmatic and question-begging. For it does not obviously follow from the fact that God must choose between various previously given essences that these essences cannot be related via a real but noncausal connection.

Yet even if one were to grant Crusius the above objection against Pre-established Harmony, Crusius has not excluded Wolff's version of Pre-established Harmony. That is, one might still think that although God cannot be directly responsible for the real connection between substances, perhaps God can be indirectly responsible for such a connection due to the fact that He creates substances that are "directed toward" every other substance. In other words, Wolff could maintain that each finite substance is "directed toward" all others and this directedness constitutes a real connection. Crusius seems to anticipate this move and replies that such a defender of Pre-established Harmony cannot "fabricate a special class of connection which one would call the metaphysical [class], and which is to consist in the one thing representing the other, for then the original concept of real connection is abandoned."(92) Yet it seems simply false to claim that `directed toward' must be interpreted as `representing' (which presumably makes the connection ideal)(93) and dogmatic to assert that a proponent of Pre-established Harmony cannot posit a real connection between substances. Why can one not say, as was suggested above, that God simply stipulates that two arbitrary sets of objects are distinct possible worlds?(94) Because Crusius defines a real connection negatively as any connection that does not exist in thought alone (that is, that exists outside thought), in order for him to substantiate his claim that real connection implies physical influx, he must exclude all other possible nonideal connections, a task he does not seriously undertake, much less accomplish.(95) Thus Crusius's argument is essentially incomplete, though still rather sophisticated in a way that Gottsched's and even Knutzen's are not.(96)

Although Crusius's arguments for Physical Influx in the Entwurf may not be convincing, he contributes to the debate between the proponents of Pre-established Harmony and Physical Influx in a number of other ways. Besides presenting the new line of argumentation considered above, he also responds to the traditional objections levied by Leibuiz and Wolff against the intelligibility of Physical Influx, and he develops the notion of basic forces further than earlier proponents of Physical Influx do.

Consider three objections proponents of Pre-established Harmony might raise and Crusius's responses.

The first objection against Physical Influx is that at/owing minds to act on bodies would turn minds into matter. The idea underlying this objection is that if mind and matter can act on each other, then they must not be radically distinct (as Descartes thinks they are). But if they are not radically distinct, then there is no essential difference between the two; mind is essentially the same as matter. Crusius replies to this objection that although mind and matter share a property, namely the general capacity (General-Eigenschaft) to move, the fact that they share a property does not imply that there are no relevant differences between mind and matter. For the capacity to move lies in the general essence (General-Wesen) of mind and matter, rather than in each one's specific difference (Differential-Wesen), which is what accounts for the differences between mind and matter.

The second objection states that it is not possible for a mind to have the capacity to move a body, since that would violate a mind's basic essence (Grund-Wesen) as a thinking thing. His response to this objection is essentially the same as to the first objection. One can explain the capacity of a mind to move a body if one considers the general essence of a mind.(97) Whereas the error underlying the first objection stems from ignoring the specific difference between mind and matter, the error in this case arises from ignoring their general essence.

The third objection Crusius considers is the traditional objection raised against Physical Influx that Physical Influx would violate both the law of the conservation of motion and the law of the conservation of moving forces. Crusius bites the bullet and rejects as impossible these particular laws, noting that if they were true, the absurd result would follow that minds could not cause any motion and that matter would not be able to fulfill the purpose for which God intended it, namely as a means to rational and free beings.(98) Thus Crusius turns the argument around and challenges the conservation laws.(99)

Crusius is also important insofar as he develops a detailed ontological foundation for Physical Influx.(100) For the proponent of Pre-established Harmony it is sufficient to endow each substance with a single force that is responsible for unfolding itself (that is, the substance) from one state to the next. Although Leibniz adds further forces, such as the representational power and the active and passive dynamical forces, they are not added due to the conditions of causality. In short, in order to maintain intrasubstantial causation, only a single force is required. With Physical Influx, however, the situation is entirely different. As Gottsched and Knutzen both demonstrate, a substance must have the force to act directly on other substances, and Knutzen argues that two forces are necessary. However, neither Gottsched nor Knutzen develops a sophisticated and detailed account of such a force, although such an account is required if one is to have a fully developed account of physical influx. Crusius is important because he provides just such an account.

At [subsections]79-81 of the Entwurf Crusius provides an explicit and detailed account of basic forces. Crusius distinguishes forces as follows:

Whatever a cause contributes to the production of an effect, it

accomplishes either 1) through its mere existence because through it

the existence, or a certain manner of existing, of another thing is made

possible or impossible or necessary.... Such causes are called

existential-grounds. [sections]36 The force thereof can be called the

inefficacious capacity of an existential ground (facultas existentialis)....

Or 2) the cause acts due to an inner property of its essence which is

now directed toward the production of this effect: Thus, one attributes

to it an activity or self-activity. It is called an active cause and its force

an active force (Facultas actiua). Thus, an active force is a property

connected to a substance belonging to its inner essence due to which

something else is actual through it or comes to be....

[sections] 80. The difficulty found in an object of accepting the

action of a cause is called the reaction or resistance....

[sections] 81. Among active substances an activity can depend in

turn on another of which it is an effect. But this series cannot proceed

infinitely, but rather one must ultimately come to first actions that arise

from the force of subjects not through another action but rather

immediately and are nothing other than the application of the first basic

forces themselves. I want to call these basic activities (actiones

primas). Two species of these are conceivable. First, such basic

activities that persist due to the essence of the substance and that

constitute the inner essence of the active substances.... Further there

is such a species of basic activities that do not constantly act.(101)

Crusius proceeds to distinguish the notion of basic forces into various further headings. However, we can already see that he has developed a much more sophisticated model of physical influx than either Gottsched or Knutzen.(102) For he has proposed a full-blown account of Physical Influx, not just a sketch or an outline.

The Weg zur Gewi[beta]heit In his Weg zur Gewi[beta]heit(103) Crusius not only develops further objections to Pre-established Harmony on the basis of the general metaphysics presented in the Entwurf,(104) but, more importantly, he also explains in greater detail how Physical Influx applies to the mind-body relationship. First, like Gottsched and Knutzen, he rejects the idea that accidents could be transferred from the mind to the body or vice versa, since "ideas are mental activities, which are neither motions nor possible through motions." He also adds that ideas are not "a special class of things that would be an intermediary between a substance and an accident"(105) (though he does not clarify what their positive ontological status is). Instead, Crusius attempts to address in as much detail as possible how the mind and the body act on each other, given that it is not through a transfer of accidents. Accordingly, Crusius states that

a real action cannot however consist in the fact that motions in the body preceding the sensation bring about the sensation-idea For that would be contradictory because there would be more in the effect than in the cause.... For just that reason an idea cannot be either the proximate or the sufficient cause of a motion. For it conflicts with our understanding of an idea because an idea is only an activity through which something is represented in the understanding, but not something from which an effect of the soul outside itself is considered possible. Consequently, either a motion must be only a condition upon whose presence an idea arises by means of a mental force whose efficacy, however, is tied to the motion; or the motion must arise as a byproduct from the efficacy of such a mental force as is awakened at the same time through the liveliness of another mental force as through its condition.(106)

Crusius explains this model in more detail as follows: "The motion in the instruments of the external senses causes a motion of the substance of the soul. And this motion of the substance of the soul has been made by God, by means of certain laws of actions in nature, into the condition under which certain mental forces, which are the true efficacious causes of representations, become lively and efficacious."(107) Crusius sees the need for a motion of the substance of the soul because "a motion can bring about nothing other than another motion. Consequently, in this way nothing other than a motion of the substance of the soul can be caused which can thus be only the condition of the sensation-idea that arises."(108) Further, "with this motion [of the substance of the soul] the matter that immediately surrounds the soul, which are presumably the life spirits, must be able to yield easily and move out of the way."(109) In short, motions can cause only motions so that if the body is to act on the soul, then the soul must be in motion. The soul's motion is then in some way a necessary condition for its mental activity. In this way Crusius develops a more detailed solution to the mind body problem that is sensitive to the kinds of demands that one would want to place on the causal powers of minds and bodies.(110)

IV

Summary. In sum, we can see a significant degree of development from Gottsched through Knutzen to Crusius insofar as each develops a model of physical influx in increasing detail in terms of a substance's capacity to act on other substances, thereby responding to one of the central criticisms raised by proponents of Pre-established Harmony. We have also seen that these proponents of Physical Influx are capable of developing interesting arguments for their position, arguments that are sensitive to Leibnizian principles. Further, these developments are not lost on one rather significant philosopher, off working away in East Prussia: Kant.(111) In his pre-Critical period (starting as early as the True Estimation of Living Forces [1746], but continuing through the Nova dilucidatio [1755] and the Inaugural Dissertation [1770]) Kant develops increasingly sophisticated arguments for his own version of Physical Influx. (112) However, if one were to move directly from Leibniz to Hume's critique of the very notion of causality, this rich and interesting story would be missed.(113) Correspondence to: Department of Philosophy, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061. (1) See, for example, Louis Loeb, From Descartes to Hume. Continental Metaphysics and the Development of Modern Philosophy (Ithaca: Cornell University Press, 1981), and Frederick Copleston, A History of Philosophy (New York: Image, 1959-1960). Exceptions are Max Wundt, Die deutsche Schulphilosophie im Zeitalter der Aufklarung (1945; reprint, Hildesheim: Olms. 1964); John Yolton, Locke and French Materialism (Oxford: Oxford University Press, 1991); and Karl Ameriks, "The Critique of Metaphysics: Kant and Traditional Ontology," in The Cambridge Companion to Kant, ed. Paul Guyer (Cambridge: Cambridge University Press, 1992), 249-79. (2) See Eric Watkins, "Kant's Third Analogy of Experience," Kant-Studien (forthcoming) and Eric Watkins, "Kant's Theory of Physical Influx," Archiv fur Geschichte der Philosophie 77 (1995): 285-324 for correctives to this view. (3) Eileen O'Neill considers the historical development of this doctrine up to Leibniz, in her "Influxus Physicus," in Causation in Early Modern Philosophy: Cartesianism, Occasionalism, and Preestablished Harmony, ed. Steven Nadler (University Park: Pennsylvania State University Press, 1993), 27-55. (4) `Pre-established Harmony', `Occasionalism', and `Physical Influx' refer to the theories of pre-established harmony, occasionalism, and physical influx. I should also note that Physical Influx is not a theory that applies only to material substances. Accordingly, the term `physical' in physical influx should be taken not literally (as corporeal), but rather as natural (as opposed to hyperphysical or supernatural). It is worth noting that physical influx is also sometimes contrasted with moral influx. Cf. Johann Peter Reusch, Systema metaphysicum (Jena, 1735), [sections]264. (5) Unless otherwise noted, `substance' refers to finite (that is, non-divine) substances along with their natural (non-miraculous) properties. (6) It is also the way in which they were generally understood in the debate in early eighteenth-century Germany. (7) Cf. A New System of the Nature and Communication of Substances, and of the Union of the Soul and Body, in Philosophical Essays, ed. and trans. Roger Ariew and Daniel Garber (Indianapolis: Hackett, 1989), 138-45, esp. 143-4. Unless otherwise noted, all quotations from Leibniz will be from the Philosophical Essays and referred to by "PE." It should be noted (against Leibniz) that it is not clear that any Scholastic ever held such a model of physical influx. Although Suarez at times uses the term `influere', he certainly does not subscribe to this model. (8) Cf. [sections]80 of the Monadology (PE, 223). For a helpful discussion of this issue, see Daniel Garber, "Leibniz: physics and philosophy," in The Cambridge Companion to Leibniz, ed. Nicholas Jolley (Cambridge: Cambridge University Press, 1994), 270-352; and Martha Bolton, "Locke and Leibniz on a Dilemma for Mechanism: Mind-Body Causality." Paper presented at the Midwest Seminar in the History of Early Modern Philosophy, Purdue, December 5, 1994. (9) Cf. A New System of Nature (PE, esp. 143-5). (10) For a discussion of Leibniz's conception of substance, see Christia Mercer and Robert Sleigh, "Metaphysics: The early period to the Discourse on Metaphysics," in The Cambridge Companion to Leibniz, 67-123. (11) See, for example, Primary Truths (PE, 32). (12) Franz Budde, Georg Walch, and, to a lesser extent, Andreas Rudiger, to mention only the most important Pietists directly engaged in the dispute. (13) For the full story, see Wolff, Eigene Lebensbeschreibung (Leipzig, 1841), 28; Wundt, Die deutsche Schulphilosophie, 230-64; and Eduard Zeller, "Wolff's Vertreibung aus Halle; der Kampf des Pietismus mit der Philosophie" Preussische Jahrbucher 10 (1862): 47-72. (14) Ludwig Philipp Thummig (1697-1728) publishes his own textbook Institutiones Philosophiae Wolffianae (Frankfurt, 1725-26) which, as the title indicates, presents Wolff's philosophy in Latin. [Note: For all references to texts published prior to this century, I shall cite only the place and date of publication.] See below for more on Bilfinger's importance and authorship. Johann Peter Reusch (1691-1754) publishes two textbooks entitled Systema logicum and Systema metaphysicum (both in Jena, 1734 and 1735 respectively). Friedrich Christian Baumeister (1709-85) publishes Institutiones philosophiae rationalis (Wittenberg, 1735), Philosophia definitiva, (6th ed.; Wittenberg, 1743) and Institutiones metaphysicae (Wittenberg, 1743). Alexander Gottlieb Baumgarten (1714-62) publishes Metaphysica (Halle, 1739), Acroasis logica (Halle, 1761), and Aesthetica (Frankfurt, 1750). Georg Friedrich Meier, in addition to translating Baumgarten's Acroasis Logica into German, authors Beweis der vorherbestimmten Harmonie (Halle, 1739) and a number of specific treatises, such as Beweis, da[beta] keine Materie dencken konne (2d ed.; Halle, 1751). Samuel Christian Hollmann publishes his three-volume textbook, Institutiones philosophicae, from 172734 and a number of other, smaller works during the 1730s, including correspondence with Bilfinger and Schreiber. (15) While the situation is complicated by other factors, it is relevant to note that a similar debate arises in both England and France. And, at least in France, it seems to have been raised in part by the German debate, given that it begins only a short time after the debate was raging in Germany. Cf. Yolton, Locke and French Materialism. In England, it was Locke's suggestion that matter might think that complicated the debate. Thus it seems to be the case both that the debate was Europe-wide and that Germany was one of its principal sources; this underscores its historical importance for modern philosophy as a whole. (16) For a more comprehensive account of both this particular issue and related ones, see Eric Watkins, "From Pre-established Harmony to Physical Influx: The Reception of Leibniz in Early Eighteenth-Century Germany," in Leibniz and the Sciences, ed. Roger Ariew and Daniel Garber (Chicago: University of Chicago Press, forthcoming). (17) Rudiger, who is loosely affiliated with the Pietists as well as with Thomasius, was Crusius's teacher. (18) Both Gottsched's dissertations and his Weltweisheit were originally published in Leipzig. (19) It is unclear whether these objections were actually made by any Cartesians in this form against Physical Influx, since Gottsched cites only Descartes's Principia philosophiae (Amsterdam, 1644). (20) Gottsched, Vindiciarum systematic influxus physici, pt. 1 (1729), 34-5. (21) Descartes holds that the quantity of motion (that is, mv) is conserved, whereas Leibniz argues that living forces (that is, [mv.sup.2]) are conserved. Cf. Leibniz, Specimen dynamicum in PE, esp. 121, and the Discourse on Metaphysics [sections]17 in PE, 49-51. (22) I suspect that this dichotomy between official and unofficial positions is caused by Gottsched's conflicting desires (1) to publish a popularization of Wolff's philosophy (which maintains Pre-established Harmony) and (2) to present what he believes to be true (Physical Influx). Gottsched attempts to resolve the tension between these desires by not taking an official position on the issue, while still making his views known. Benno Erdmann interprets Gottsched's statements in such a way that Gottsched was either

(*) The Development of Physical Influx in Early Eighteenth-Century Germany: Gottsched, Knutzen, and Crusius" has been selected as the winner for 1994 of the Dissertation Essay Competition, which is sponsored by The Philosophy Education Society, Incorporated, publisher of the Review of Metaphysics. Details of the Competition are listed in the September 1995 issue. confused or simply could not decide: "A mind like Gottsched could never make it to definitive clarity": "Zu entschiedener Klarheit zwar konnte ein Geist, wie Gottsched, nie kommen"; Benno Erdmann, Martin Knutzen und seine Zeit (Hildesheim, 1876), 81. (23) "Keine derselben ist noch vollkommen erklaret oder demonstriret; eine jede davon hat noch ihre Schwierigkeiten: es kann sich also ein jeder an diejenige halter, die ihm am besten gefallt. Mir ist es indessen allezeit vorgekommen: daB man nicht eher Ursache habe, die alleralteste und gemeineste Meynung vom naturlichen Einflusse zu verwerfen; bis man sie vollkommen widerleget, und ihre Unmoglichkeit erwiesen haben wird. Dieses aber ist, noch zur Zeit, von niemanden geschehen"; Gottsched, Erste Grunde der gesammten Weltweisheit, [sections]1077, Ausgewahlte Werke, vol. 5, pt. 1, 6th ed. (Berlin: de Gruyter, 1983), 586. Note: all passages quoted from the sixth edition are present in the first edition, except where differences are explicitly noted. Also, all translations are my own. (24) Gottsched, Erste Grunde der gesammten Weltweisheit, [subsections]1078-9. In [sections]1079 of the sixth edition of the Weltweisheit, Gottsched refers to Knutzen's position and notes that Knutzen expounds in more detail the position that he (Gottsched) has defended since 1729 in his dissertations. Erdmann argues that Knutzen develops his view independently of Gottsched; see Erdmann, Martin Knutzen, 82. It should also be noted, in light of the discussion below concerning Gottsched's position on the general cosmological issue, that both this point and the next do not seem to bear on the general issue. (25) Ibid., 582. (26) Knutzen will give a very similar response to the first of these objections (see Systema Causarum efficientium [Leipzig] [subsections]48-49), and he will give a similar response to an objection that differs slightly from the second objection, namely that Physical Influx implies the falsity of the immortality of the soul ([sections]57). (27) "Die Seele hat namlich eine Bemuhung, neue Empfindungen hervor zu bringen (1051. [sections].). Diese kann sie nicht haben, wenn ihr Korper nicht eine solche Lage und Stellung in der Welt hat, daB, vermittelst der sinnlichen GliedmaBen, die materialischen Bilder im Gehirne erwecket werden konnen. Also strebet sie denn zu gleicher Zeit, nach dieser veranderten Stellung oder Lage des Korpers"; Gottsched, Weltweisheit, 587. (28) "Es sind schon in den flussigen Theilen des Leibes so viele Krafte vorhanden: daB selbige gleichsam nur eine Aufweckung und Bestimmung bedorfen, wenn sie wirken sollen. Konnen wir es aber noch nicht erklaren, wie es damn' zugehe, daB die Seele irgend den Nervensaft in Bewegung brings; so konnen wir es ja auch in den Korpern noch nicht vollig begreifen, wie eine an die andere stoBende Kugel dieselbe in Bewegung setzet. Denn da in alien Puncten, wo sich dieselben beruhren, Monaden oder Elemente vorhanden sind: so mussen diese doch in einander wirken, und die Bewegung fortpflanzen konnen, ob wir gleich nicht wissen wie"; ibid., [sections]1081, 587-8. (29) It is difficult to discern from this passage whether Gottsched is making the further claim that two forces must be exercised for a change to occur (as Knutzen will argue) or whether one suffices. (30) "Konnte aber die Seele alle Empfindungen auch ohne denselben haben: wozu ware ihr ein Leib nutze? Ein Idealist haste sodann eine weit bessere Meynung; well er durch das Laugnen der Korper, unzahlige Schwierigkeiten uberhoben wurde"; Gottsched, Weltweisheit,, [sections]1082, 588. It is worth noting that this objection is frequently cited in the ensuing debate (for instance, by Reusch and, below, Crusius). (31) Somehow Gottsched seems not to have understood that, properly speaking, Leibniz is an idealist. (32) "Doch ich gebe dieses alles nur fur bloBe MuthmaBungen aus, und lasse es dahin gestellt sein: welche Meynung bey einem reifern Erkenntnisse der Seele und des Leibes, mit der Zeit die Oberhand behalten wird"; ibid., 588. (33) Benno Erdmann, in Martin Knutzen und seine Zeit, gives a nice, if not always entirely accurate, account of Knutzen and his historical setting, including an account of Knutzen's other works. For example, Erdmann notes that Knutzen's Philosophischer Beweis von der Wahrheit der Christlichen Religionis reprinted five times and is even translated into Danish (p. 53). (34) For information on which of Leibniz's works were published and available at what date, see Emile Ravier, Bibliographie de Oevres de Leibniz (Hildesheim: Georg Olms, 1966). (35) For one account of the differences between Wolff and Leibniz, see Charles Corr, "C. Wolff and Leibniz," Journal of the History of Ideas 36 (1975): 241-62. (36) How the position Knutzen is attacking is Leibnizian will be demonstrated in footnotes accompanying the relevant argument. What we shall find is that Knutzen gives a number of different arguments at different levels of generality so that the position he is attacking will be Leibnizian in some way, whether it be the "middle" or "later" Leibniz. (37) It is somewhat unfortunate that Knutzen seems to focus on the New System of Nature, since Leibniz's position in that treatise is somewhere between his middle and later positions. (38) Knutzen's argument is quite similar to Leibniz's in the New System of Nature. For Knutzen argues as follows:

"[sections]. XX. The existence of monads in bodies or the composition of bodies from monads is shown.

Bodies consist of simples or monads. Bodies are composite entities ([sections]. 19.), and therefore consist of parts (according to the same [sections]). Either these parts are in turn composite, that is, they will have other parts that again have others and so on to infinity, or one must reach at last parts that do not consist of others. If the former, there is an infinite number of parts the existence of which implies a contradiction (as is demonstrated in the diss. de Aeternitate Mundi impossibili [sections]. 21): therefore, a body is composed of parts that do not have other parts. Therefore, it consists of simplex, or monads ([sections]. 18)." (39) Cf. [sections]XXVII. "It is demonstrated that simple elements are in a place and are moved, although they do not fill a space." (40) "[sections]. XXVIII. Vis seipsam mouendi inuoluit vim alia quoque mouendi realiter.

Vis mouendi, quae efficit, vt ens quodpiam locum suum proprium mutes, sine vi mouendi, res alias, quibus cingitur, concipi nequit, sed ista posita haec simul ponatur, necesse est. Vis enim mouendi, quae efficit, vt ens locum suum proprium mutes, non est, nisi conatus, hunc suum mutandi locum ([sections]. 24.) i. e. occupandi locum ab eo, quem iam occupat, dinersum et quidem eidem continuum ([sections]. cit.). Sed coexistentia alia, quae vbique mobile cingunt, loca ista a loco mobilis diuersa obtinent; duo autem diuersa entia simul in eodem loco esse nequeunt ([sections]. 23.): ens ergo vi se ipsum mouendi praeditum, res alias loco pellere nitetur, si illae resistant. Quod si vero etiam sponte cedere supponantur, tamen id quod in nisu tall, qui requiritur ad motum extra se perficiendum, siue alias res loco pellendas, in motu progressiuo iam adest; cum resistentia sit tantum cause occasionalis motus, nec vi intrinsecae quicquam addat: Ens ergo, quod se ipsum moues, conatu gaudet mutandi locum coexistentium seu vi mouendi res alias ([sections]. 24.). Vis ergo, se ipsum mouendi, sine vi mouendi res alias concipi nequit, sed ista posita, haec ponitur simul." (41) Note that Knutzen formulates this argument quite generally so as to pertain to any being of which a Leibnizian will claim that it can change its own place. Thus the argument will certainly apply to bodies, to corporeal substances of Leibniz's middle period, and perhaps even to the monads of the later Leibniz (since monads are in some sense in a place and responsible for the changes that occur in bodies, so that one could say that they change the place of their body). For a discussion of Leibniz's conception of substance in his middle and later periods, see Robert Sleigh, Leibniz and Arnauld, (New Haven: Yale University Press, 1990), 98-104; Christia Mercer and Robert Sleigh, "Metaphysics: The early period to the Discourse on Metaphysics," in The Cambridge Companion to Leibniz; and Donald Rutherford, "Metaphysics: The late period," in ibid. (42) As the argument stands, it is, of course, incomplete. For Knutzen simply accepts without argument that every being is surrounded in all directions, that is, that there is no void. Accordingly, the argument might seem to stand in need of substantial supplementation. However, the argument would presumably have appeared plausible to Leibniz because he accepts the Principle of Sufficient Reason which he then takes to exclude the possibility of a void; cf. Primary Truths in PE, 33. In fact, Leibniz rejects the void for further reasons as well; cf. Specimen dynamicum in PE, 130. (43) In fact, ar. anonymous reviewer of this work makes the same objection to Knutzen's argument. Cf. Zuverla[beta]ige Nachrichten vom dem gegenwartigen Zustande, Veranderung und Wachstum der Wissenschaften, Teil 73 (Leipzig, 1746), 48-67, esp. 50-3. (44) Knutzen is quite explicit about this model. In [sections]44, responding to the charge that Physical Influx is merely the flowing out and metamorphosis of motion and ideas, Knutzen states the following: "While the body acts on the mind according to the system of physical influx, it does not pour ideas of external things into the mind, nor the force of representation; but rather it modifies only the force of the mind and its substance in such a grounded way that representation is caused in the mind. But the mind, when it acts on the body, does not pour a moving force into it, but rather only modifies and directs with its actions those things to the extent that are present in corporeal elements in such a way that finally motion is produced in the body. For ideas and the force of representation are either accidents or substances. If they are accidents: they cannot be poured into the mind by the body and they cannot be transferred into the mind by a certain local motion from the body. For accidents do not migrate from subject to subject ([section]. 791. Ontol.). But if you suppose that they are substances: similarly such a transition cannot be granted; because the mind is a simple substance ([sections]. 18.), but such a first substance cannot be the receptacle of a number of other substances. Therefore, neither ideas nor the forces of representation can be poured from the body into the mind. However, because representations of external things appear in the mind through the action of the body ([sections]. 40. not.): nothing remains other than that the body, while it is acting on the mind, modifies its force and substance in such a way that representations of external things in fact appear or are caused in the mind. For a similar reason it can be shown that no moving force can be transferred from the mind to the body: and so through the action of the mind only those forces that the moderns have shown to be present in the elements [of the body] ([sections]. 196. Cosmol.) are modified and directed for a certain reason in such a way that determinate motion is finally produced in the body through the determination of these forces": "Dum corpus in mentem agit vi systematic physic) influxus, neque menti rerum externarum ideas infundit, neque vim repraesentatricem; sed modo vim mentis eiusdemque substantiam tall ratione modificat, ut repraesentatio in mente oriatur. Mens vero, dum in corpus agit, nullam eidem vim motricem infundit; sed eam tantum, quae corporis elementis inest, ita actione sua modificat ac dirigit, ut motus demum in corpore producatur. Ideae enim ac vis repraesentatrix vel accidentia sunt vel substantiae. Si sunt accidentia: menti a corpore infundi ac locali quodam motu e corpore in mentem transire nequeunt; accidentia enim e subiecto non migrant in subiectum ([sections]. 791. Ontol.). Si vero substantial esse supponas: similiter eiusmodi transitus concedi nequit, cum mens sit substantia simplex [sections]. 18.), talis vero substantia alterius vel plurimarum aliarum substantiarum receptaculum esse nequeat. Ergo neque ideae, neque vis representatrix e corpore in mentem transfundi possunt. Cum tamen per corporis actionem repraesentationes rerum externarum in mente prodeant ([sections]. 40. not.): nil superest, quam ut corpus, dum in mentem agit, vim eius ac substantiam ita modificet, vt repraesentationes rerum externarum in mente reuera prodeant seu excitentur. Simili ratione evinci potest, quod nulla vis motrix ex mente transeat in corpus: adeoque mentis actione eae tantummodo vires, quas eiusdem elementis inesse demonstrarunt recentiores ([sections]. 196. Cosmol.), certa ratione modificentur ac dirigantur, vt sic demum harum virium determinatione determinatus in corpore motus producatur"; Knutzen, Systema Causarum efficientium, 145-7. (45) For Leibniz a ground is ideal if it exists solely in a monad's representations. Real grounds can exist independently of the representations of a monad. See Monadology, in PE, 219 and Letter to Des Bosses, in PE, 199. (46) See, for example, the New System, in PE, 143. (47) In a sense, no relationship would hold at all between various substances, if one grants that there are no relationships between nonexistent substances. (48) "Agere dicitur ens, quando rationem in se continet existentiae (mutationis) cuiusdam rei"; Knutzen, Systema Causarum efficientium, [sections]21, p. 78. (49) For a discussion of the expression thesis, see Robert Sleigh, Leibniz and Arnauld, 170. (50) Knutzen does not take Leibniz's thesis about the "equivalence of hypotheses" into account. This omission may not be of consequence, if the equivalence of hypotheses is taken as a purely epistemological claim (that we cannot know which of any two bodies is in motion) as opposed to the metaphysical claim (that bodies are not in motion, from which the epistemological claim immediately follows). (51) "Idem quoque aliter posses demonstrari: Simplicia elementaria sunt impenetrabilia, ex sententia Leibnitii, qui substantiae finitas omnes impenetrabiles asserit. videatur eius Epist. ad C. Wagnerum p. 201. Tom. I. Epist. Edit. Kortholtianae. Hinc fieri non potest, vt vna sit in loco alterius. Ergo datur aliquid reale, vi cuius vnum simplex alind excludit ac contra nititur, ne in suum irruat locum. Cum enim moueri simplicia certissimum sit ([sections]. 27.) neque diuersa simplicia secundum contrariam directionis lineam moueri, adeoque sibi inuicem occurrere impossibile sit, imo etiam id quod ex conflictu corporum et occursu eorundem colligimus, reuera contraria directione contra se inuicem ferantur; sequitur in eo casu statuendum, aut simplicia se inuicem penetrare, quod contra asserta Leibnitii; aut si inuicem resistant; in se inuicem agere. Q.e.d."; Knutzen, Systema Causarum efficientium, [sections]29, p. 95. (52) Knutzen formulates this argument so as to apply to substances that have resistance or impenetrability. Thus, again, Knutzen's argument is so general that it applies to bodies, corporeal substances (in the middle Leibniz), and again, though this is less clear, perhaps even (the later Leibniz's) monads (since Leibniz may hold that two monads cannot be in the same place). (53) It is worth pointing out that in [sections]39 Knutzen explicitly applies these first two arguments to the mind-body relationship. (54) It is worth noting that Knutzen (like Leibniz before him and Crusius and Kant after him) considers the issue of causality both in its completely general form (that is, for any substances whatsoever) and in the specific guise of the mind-body problem, whereas many parties to the dispute limit themselves to discussing only the mind-body problem. As a result, Knutzen's position attains a greater degree of sophistication. (55) "Perfectio, quae nullam per se infers limitationem, seu, quae cum omnitudine possibilium (vt loquuntur Scholastici) consistere potest, perfectio dicitur absolute talis seu simpliciter simplex. In Theologia natural) autem demonstratur, quaecunque in Deo T. O. M. locum inueniunt, perfectiones esse simpliciter simplices, nec, nisi cum limitationibus seu imperfectionibus, ullam inuoluere repugnantiam"; Knutzen, Systema Causarum efficientium, [sections]33, p. 107. (Note: T. O. M. is an abbreviation that stands for ter optimus maximus or "thrice greatest most powerful." Since such an abbreviation is not currently common, I have omitted it wherever it would occur in the translation but not in the original Latin.) That Knutzen cites Bilfinger (and Canz) in the explanatory passage to this definition indicates that he does not take himself to be positing anything that would be controversial to the Leibnizians. (56) "Influxus Physicus est possibilis. Influxus physicus mentis in simplicia corporis et vicissim eorundem in mentem actione absoluitur ([sections]. 32.). Si adeoque possibilitas physic) influxus euincenda, ostendendum, eiusmodi mentis extra se actionem in alia simplicia nullam inuoluere contradictionem ([sections]. 85. ontol.): perpendamus adeoque, num quicquam in mente reperire liceat, quad eiusdem action) in res external repugnet. Quae in mente inuenimus, huc potissimum redeunt, quod mens sit ens simplex, nec non, quod sit ens perceptinum seu percipiens, idque longe eminentioris gradus, quam simplicia elementaria, siquidem est distincte perceptiuum seu intellectu et voluntate praeditum ([sections]. 17. 18.). Simplicitati mentis actio in res external repugnare nequit, cum non modo Deus T. O. M. extra se agat (per Princip. Theol. N.), sed etiam simplicia elementaria agent in se inuicem ([sections]. 29.). Neque quatenus est ens perceptiuum seu percipiens actio haec menti repugnare potest, cum simplicia elementaria rerum externarum perceptione gaudeant ([sections]. 31.); quibus tamen actio eiusmodi denegari nequit ([sections] 2.9.). The Niligitor superest, quam eminens illa perfectio, qua mens humane a simplicibus percipientibus inferioribus discernitur, ac quae intelligendi ac volendi facultatem in mente pooit, cud, si actio externa mentis non repugnat, influxus possibilitas extra dubium erit constitute. Est vero actio in res external perfectio simpliciter simplex, cum in Deo T. O. M. locum habeas ([sections]. 33.); adeoque non nisi limitation) ac imperfection) repugnare potest ([sections]. cit.): intellectui igitur et voluntati, quae nudae perception) accedunt, quibusque simul major enti confertur perfectio repugnare nequit, cum, enti mere perceptiuo ac imperfectiori actionem eiusmodi conuenire, iam supra sit euictum. Quis ergo mentem in corpus agere posse dubitare poterit? Cum autem, simplicibus ex quibus corpus constat, actionem in alla simplicia tribuendam esse, supra sit demonstratum ([sections]. 29.); mens vero, tanquam substantia simplex, in eadem agere possit (per demonstr.): nulla erit ratio, cur simplicium corporis in mentem actionem quis iudicet impossibilem. Influxum adeoque physicum possibilem esse, constat"; Knutzen, Systema Causarum efficeintium, [sections] 34, p. 108-10. (57) "Unlike the first two arguments, this argument is more specific in its application, since it applies only to minds. However, it is clear that Knutzen's understanding of minds does not differ in any essential way from Leibniz's. (58) See Leibniz's "Quod ens perfectissimum existit" from 1676 for a passage in which he is more explicit about this point; Leibniz, Die Philosophischen Schriften, ed. Carl Gerhardt (1875-90; reprint, Berlin: Olms, 1978), 7:261-2. Please note that I am not suggesting that Kntuzen is aware of this particular passage. (59) This feature of Knutzen's account is explicitly stated in Systema Causarum efficientium, [sections]43, p. 142 and [sections]44 (for [sections]44 see note 44 above): "According to the system of physical influx the human mind is not in every respect nor specifically in thinking to be conceived of as purely passive": "Mens humana in systemate Physici influxus nec omni ex parse, nec speciatim in cogitando mere passiua est concipienda." (60) "Evincitur enim in Theologia natural): Deum T. O. M. summae ac infinitae suae sapientiae conformiter, viam eligere naturalem, brevissimam"; Knutzen, Systema Causarum efficientium, [sections]35, p. 113. (61) "nec ea, quae per pauca fieri naturaliter possum, per plura seu longior demum via absoluere"; ibid. (62) "Non tamen breuitatem viae solam vrgeo, sed viam naturaliter breuissimam"; ibid., p. 116. (63) "per ambages [a Deo sapientissimo facta supponit], cum tot artificia ad hunc consensum, tum in corpore, tum mente, producendum sint necessarie, vt omnem superent captum"; ibid., p. 117. (64) Of course, the nature of miracles is intensely debated by Leibniz and Malebranche. (65) It is worth noting that Bilfinger is influential both in Saint Petersburg and Tubingen. For more on Bilfinger's general influence, see Heinz Liebing, Zwischen Orthodoxie und Aufklarung, (Tubingen: Mohr, 1961). (66) For discussion of this work, see Joachim Kintrup, Das Leib-Seele-Problem in Georg Bernhard Bilfingers Buch "De harmonia animi et coporis humani, maxime praestabilita, ex mente illustris Leibnitii, commentatio hypothetica (1723)" in der geschichtlichen und philosophischen Zussammensichau (Munster: Munstersche Beitrage zur Geschichte und Theorie der Medizin, 1974). (67) Although Knutzen is not always as explicit as one might like, one can perhaps assume that Knutzen accepts Gottsched's position on the issue of the law of motion; accordingly, only the issue of motive forces remains. (68) "[sections]54. Objection VII. A defect in the proportion between the motion of the body and the decrees that follow from the mind.

Causes and effects are proportional amongst each other or the effects are proportional to the causes by which they are produced and the causes in turn are proportional to the effects that have been produced by them. But the forces of the mind and the motions of the body are not mutually proportional to each other. Therefore, the motions of the body are not at all produced by the force of the mind or the forces of the mind and the motions of the will in the body are not related as causes and effects amongst each other; thus, to this extent there is no influx of the body in the mind and vice versa"; Knutzen, Systema Causarum efficientium, p. 184. (69) "[sections]55. Objection VIII. that the effect is greater than its cause according to physical influx.

The whole effect is equal to the full cause. But in the system of physical influx what is considered to be whole effect is not equal to the full cause. Therefore, what is considered to be the effect in the system of physical influx is not the effect. Therefore, there is no influx of the mind on the body nor vice versa. The learned Bilfinger built a proof of the minor premise on this foundation because in physical influx the effect is greater than its cause, because sc. not only is the motion of the fluid nerves in the brain caused by motion in the sense organs, and they in turn cause the motion of another that then releases the full effect: but besides this effect and the other there is sc. representation in the mind that therefore reflects an effect greater than the cause"; Knutzen, Systema Causarum efficientium, pp. 190-1. (70) "nego minorem, sc. quod ex Physico Influxu sequatur, in conflictu corporum inter se eandem virium quantitatem haud conseruari"; Knutzen, Systema Causarum efficientium, [sections]53, p. 177. (71) "Adeoque quamdui nondum euictum est ac euinci potest, istam motus legem de conseruanda eadem virium viuarum quantitate non modo corporibus in se inuicem agentibus, sed et menti in corpus agent) et vicissim praescriptam esse; prorsus nil praesens objectio Influxui physico nocebit"; Knutzen, Systema Causarum efficientium, [sections]53, p. 178. (72) "quod sc. Corpus quodlibet perseueret in statu suo quiescendi et movendi uniformiter in directum, nisi a causa extrinseca statuary suum mutare cogatur" and "Euidentissimum igitur est, mentem in statu suo acquiescendi ac mouendi uniformiter in directum, donec ab extrinseco statuary mutare cogatur, haud permanere"; Knutzen, Systema Causarum effirientium, [sections]53, p. 182. (73) "Notandum esse in influxu physico 1) ipsam motus impressionem, qui monadibus communicatur in eisdem excitare perceptionem, nam communicatio motus non nisi per modificationem virium, quae elementis insunt et quas perceptiuas statuit Leibnitius peragi potest; adeoque vltra communicationem motus aliud nil requiritur, ad excitandum perceptionem; et quemadmodum in monadibus corporum similiter et in anima"; Knutzen, Systema Causarum efficientium, [sections]55, p. 192. (74) See also Knutzen, Systema Causarum efficientium, [sections]55, p. 195. (75) I do not intend to be taking a stand on the much-discussed issue of whether Leibniz does or does not hold phenomenalism with respect to bodies. (76) Here it is important to note that what we mean by Pre-established Harmony is the doctrine of intrasubstantial causation because sometimes Leibniz does call the concomitance between efficient and final causes Preestablished Harmony, though with a completely distinct meaning. The two doctrines are not at all logically related. (77) Certainly Occasionalism is in no way distinct from Pre-established Harmony on this point, though, if Knutzen is right, neither is Physical Influx. (78) Euler considers and rejects Pre-established Harmony in his Gedanchen von den Elementen der Korper, (Berlin, 1746); Reflexions sur l'espace et le temps, (Berlin, 1748); and Lettres a une princesse d'Allemagne sur divers sujets de physique et de philosophic (St. Petersburg, 1768-72). For Darjes, see [subsection]54-90 in Elementa Metaphysices, V. II (Jena, 1743-44) and for Plouquet, see [subsection]456-483 in Principia de Substantiis et Phaenomenis (Frankfurt, 1753 and 1764). (79) If the noncorporeal element were sufficient, the corporeal element would be superfluous. (80) Erdmann, Martin Knutzen und seine Zeit, 94-5. For, as I hope to show, although the questions change somewhat, it is still the same debate, and substantial progress is made. (81) In a preliminary version of her dissertation, Alison Laywine suggests such a line of argumentation; see Alison Laywine. "Physical Influx and the Origins of the Critical Philosophy." Ph.D. dies., University of Chicago, 1991. (82) Crusuis's degree of sophistication over, say, Wolff's is immediately apparent if one compares, for example, each one's introduction to cosmology. Both consider the concept of world in order to give a proper definition. However, whereas Wolff simply claims that one must know what a world is in order to understand what a soul is (Vernunfftige Gedancken [sections]540), Crusius presents a number of methodological points that must be kept in mind if one is to define the essence of the world, a metaphysical truth, rather than, for example, any merely contingent truth about this world (Entwurf [sections]347). (83) "eine Welt hei[beta]t eine solche reale Verknupfung endlicher Dinge, welche nicht selbst wiederum ein Theil von einer andern ist, zu welcher sie vermittelst einer realen Verknupfung gehorte"; Crusius, Entwurf, [sections]350. (84) "Wir unterscheiden eine Welt von mehrern zugleich seyenden Geschopfen oder Inbegriffen derselben, welche aber in gar keiner Verknupfung stehen. Die Welt soil etwas eines seyn, und zwar ein solches, welches auch au[beta]erhalb unserer Gedancken ein Eines ist. Daher mussen die darzu gehorigen Dinge in einer realen Verbindung stehen"; ibid., [sections]349. (85) Actually, Leibaiz does not think that we can know the truth values of counterfactuals, that is, that we can think monads in other possible worlds. Thus this problem would not arise for him. However, he is saddled with the difficulty of explaining why we cannot represent other possible ways the world could have been. (86) This latter possibility is not so straightforward because for Leibuiz (unlike Descartes) possible worlds are given in God's understanding, not determined by God's will. Accordingly, it may not be in God's power to stipulate what possible worlds are (even if it is in his power to determine which possible worlds become actual). (87) It should be noted, for later purposes as well, that Crusius does derive a number of necessary truths from the definition of the world: its finitude, its creation and hence beginning in time, the conservation of the world at every moment by God, that creation must include rational and free creatures, and so forth ([subsection]351-4). (88) "eine jedwede Vereinigung zufalliger Dinge, welche au[beta]erhalb der Gedancke eine reale undo existentialis seyn soil, auf einer Causalverknupfung der Dinge beruhen musse, vermoge deren zum wenigsten eines gegen das andere thatig wircken mu[beta], wiewohl auch beyde wechselweise gegen einander thatig seyn, und auch wechselweise voneinander leiden konnen. Denn es ist sonst nichts anders ausserhalb der Gedanke moglich, was einen Grund der Vereinigung zwischen vollstandigen Dingen abgeben ken. Sobald man dahero dieses hinweg nimmt, so mu[beta] man sie nur durch einen Begriff im Verstande vereinigen, d.i. die Dinge haben alsdenn entweder gar keine oder doch nur eine blo[beta] ideale Vereinigung. Daher kann ich z. E. nicht einraumen, da[beta] diejenigen, welche die prastabilirte Harmonie glauben, eine reale Vereinigung zwischen Leib und Seele ubrig lessen. Ihre Vereinigung ist bey Setzung dieser Meynung so gar in Absicht auf Gott selbst nur ideal. Man ken nicht einmal sagen, da[beta] sie nur vermittelst der Darzwischentretung Gottes vereinigt werden. Denn alsdenn mu[beta]te doch Gott zum wenigsten die Einrichtung des Wesens des Leibes und der Seele zugeschreiben werden konnen. Dieses konnen aber die Vertheidiger der prastabilirten Harmonie in dem rechten Leibuitzischen Verstande, nicht sagen, well sie Gott keine Ehre weiter ubrig lessen, als da[beta] er nur die Wesen der Substanzen zur Wirklichkeit gebracht, nicht aber eingerichtet habe, well alle Wesen ewig sein sollen. Es bleibt dahero eine blosse Ubereinstimmung, nicht aber eine reale Vereinigung ubrig"; Crusius, Entwurf, [sections]94. (89) It may be that Crusius is insinuating other arguments here as well. For example, his allusion to the eternity of substances (and thus the world) is a consequence he clearly believes to contradict the Principle of Contingency ([sections]33). He states the principle as follows: "that whose non-being can be thought really did not exist at one time, which one calls the Principle of Contingency": "dasjenige, dessen Nichtseyn sich denken la[beta]t, wirklich einmal nicht gewesen sey, welches man den Satz von der Zufalligkeit nennen kan." (90) Kant sometimes alludes to this kind of criticism as well; see Immanuel Kant, Gesammelte Werke, ed. Koniglich Preussische Akademie der Wissenschaften (Berlin: De Gruyter, 1902), 28:215. (91) At this point, it is appropriate to recall that Crusius advances a strongly voluntaristic position with respect to God. This position explains how Crusius can object to Leibniz in this manner. (92) "Und wenn man, um eine Ausflucht zu haben, eine besondere Classe der Vereinigung erdichtet, welche man die metaphysische nennen will, und welche darinnen bestehen soil, da[beta] ein Ding das andere vorstellet, so wird hiermit der erste Begriff der realen Vereinigung verlassen"; Crusius, Entwurf, [sections]94. (93) Also, Crusius must have known that Wolff does not specifically attribute representational powers to corporeal substances. If Crusius wants more explanation of what it means for Wolff that corporeal substances are `directed toward' all others, then his point is well taken. However, this lack of an explanation on Wolff's part does not warrant an argument to the contrary position. (94) Kripke and Putnam have shown that stipulation need not be taken as "ideal," since stipulation can be embedded in social practices with causal histories. Thus there is no a priori inference from the stipulative character to the ideal character of "directed toward," even if it is divine stipulation that is at issue. (95) This charge is not completely just, given the developments discussed below. However, he himself admits at [sections]94 of the Entwurf: "it is impossible that a finite understanding should be able to comprehend all possible kinds of connection": "es ist unmoglich, da[beta] ein endlicher Verstand alle mogliche Arten der Vereinigung sollte begreifen konnen." (96) Crusius's argument anticipates Kant's in several respects. See Watkins, "Kant's Theory of Physical Infiux." (97) In this context, Crusius adds that impenetrability is included in the general essence of the mind without noting that impenetrability and the capacity to move another body are not necessarily identical. However, in [sections]402 of the Entwurf he does suggest that impenetrability is the ground of moving another substance. (98) "For if this were the case [that is, if this law of the conservation of motion were true], minds could cause no motion; and if said, that a single sum of motion remains in the material world constantly, then no part of the motion of matter could be used for the motion of the substance of minds. But then the material world would be of no use to minds, and it would have been created completely without a purpose": "Denn wenn dieses ware, so konnten die Geister keine Bewegung verursachen; und wenn sags, da[beta] in der materialen Welt bestandig einerley Summe der Bewegung bleibe, so konnte auch kein Theil von der Bewegung der Materie auf die Bewegung der Substanz der Geister verwendet werden. Alsdenn aber ware die materiale Welt den Geistern nichst nutze, und sie ware vollig ohne Zweck erschaffen"; Crusius, Entwurf [sections]419. (99) See [sections]420 of the Entwurf for his response to the law of the conservation of motive force. (100) One can diagnose the fault of the allegedly scholastic version of Physical Influx as the failure to provide a plausible ontological foundation; "migrating accidents" are entirely implausible. (101) "Dasjenige, was eine Ursache zu Hervorbringung eines Effectes beytragt, verrichtet sie entweder 1) durch ihr blosses Daseyn, well durch dasselbe die Existenz oder eine gewisse Art zu existiren eines andern Dinges moglich oder unmoglich, oder nothwendig gemacht wird.... Wir haben solche Ursachen oben Existential-Grunde genennt. [sections]36 Die Kraft derselben kan das unwircksame Vermogen eines Existential-Grundes heissen, (facultas existentialis).... Oder 2) die Ursache wircket vermittelst einer innerlichen Eigenschaft ihres Wesens, welche jetzo zu Hervorbringung dieses Effectes abgerichtet ist: So schreibet man ihr eine Activitat oder Selbstthatigkeit zu. Sie hei[beta]t eine thatige Ursache und ihre Kraft eine thatige Kraft, (Facultas actina) Es ist also eine thatige Kraft eine solche an eine Substanz verknupfte Eigenschaft ihres innerlichen Wesens, vermogen deren durch sie etwas anderes wircklich ist, oder entstehet. . .

"[sections] 80. Die in einem Object befindliche Schwierigkeit, die Action einer Ursache anzunehmen heiet die Reaction, oder der Wiederstand.

"[sections] 81. In den thatigen Substanzen ken eine Thatigkeit wiederum von einer andern abhangen, von welcher sie eine Wirckung ist. Diese Reihe aber ken nicht unendlich fortgehen, sondern man mu[beta] zoletzt auf erste Actionen kommen, welche aus der Kraft der Subjecte nicht vermittelst einer andern Action, sondern unmittelbar entspringen, und nichts anders als die Anwendung der er-ersten Grundkrafte selbst sind. Ich will dieselben Grund-Thatigkeiten (actiones primas) nennen. Es lessen sich zweyerley Gattungen derselben dencken. Erstlich solche Grund-Thatigkeiten, welche vermoge des Wesens der Substanz bestandig fortdauern, und welche eben das innerliche Wesen der thatigen Substanzen ausmachen.... Ferner la[beta]t sich auch eine solche Art von Grund-Thatigkeiten dencken, welche nicht bestandig geschehen." (102) It is possible that Crusius's sophistication is partially due to his acquaintance with late scholastics such as Suarez. (103) Crusius, Weg zur Gewi[beta]heit und Zuverla[beta]gheit der menschlichen Erkenntnis (Leipzig, 1747). (104) At [subsections]71-6, pp. 124-36 of the Entwurf, Crusius develops a series of further objections to Pre-established Harmony showing both a priori and a posterior) that Pre-established Harmony is neither true, probable, nor possible. (105) "Denn die Ideen sind geistige Thatigkeiten, welche weder Bewegungen sind, noch durch Bewegungen moglich sind.... eine besondere Art von Dingen, welche zwischen einer Substanz und einem Accidente das Mittel waren"; ibid., [sections]77, p. 140-1. (106) "Diese reale Einwirkung aber ken nicht darinnen bestehen, da[beta] die vor der Empfindung vorhergehenden Bewegungen im Korper die Emptindungsidee selbst hervorbrachten. Denn es ware widersprechend, well in der Wirkung mehr, als in der Ursache ware.... Aus eben dem Grunde ken auch eine Idee keine nachste, auch keine zureichende Ursache einer Bewegung seyn. Denn es streitet mit dem, was wir bey einer Idee denken, well in ihr nur eine Thatigkeit ist, wodurch etwas im Verstande vorgestellet wird, nicht aber etwas, worause eine Wirksamkeit der Seele ausser sich als moglich begriffen wurde. Folglich mu[beta] entweder die Bewegung nur eine Bedingung seyn, bey deren Gegenwart, die Idee vermittelst einer geistigen Kraft entstehet, deren Wirksamkeit aber an die Bewegung gebunden ist; oder die Bewegung mu[beta] als ein Nebenumstand aus der Wirksamkeit einer solchen geistigen Kraft entstehen, welche durch die Lebhaftigkeit einer anderen geistigen Kraft, als durch ihre Bedingung zugleich erwecket wird"; Crusius, Entwurf, [sections]79, pp. 144-5. (107) "Die Bewegung in den Werkzeugen der ausserlichen Sinne verursachet eine Bewegung der Substanz der Seele. Und diese Bewegung der Substanz der Seele ist vermittelst gewisser Gesetze der Actionen in der Natur von Gott zur Bedingung gemacht worden, unter welcher gewisse geistige Krafte, welche die wahre wirkende Ursache der Vorstellungen sind, lebhaft und wirksam werden"; ibid., [sections]80, p. 145. (108) "Nun ken eine Bewegung nichts anders als wiederum eine Bewegung hervorbringen. Folglich ken hierdurch nichts anders als eine Bewegung der Substanz der Seele verursachet werden, welche dahero nur die Bedingung der entstehenden Empfindungsidee seyn kann"; ibid., p. 146. (109) "Bey dieser Bewegung mussen die Materien, welche die Seele zunachst umgeben, welches vermuthlich die Lebensgeister sind, bequem nachgeben und ausweichen konnen"; ibid. (110) This solution does have its costs. For instance, the soul would seem to be at least partially material since it moves, and the problem of mindbody interaction is simply pushed back into the depths of the soul because it remains unclear how the motions of the substance of the soul can be related to the soul's mental activities. (111) Indeed, they are not lost on many of the philosophers from this period. For instance, perhaps the most highly regarded philosopher in Germany in the 1770s, Moses Mendelssohn, defended Pre-established Harmony (in his Philosophische Gesprache [Berlin, 1755]). For an account of how Mendelssohn is important in other ways to the development of Kant's views, see Paul Guyer, "Mendelssohn and Kant: One Source of the Critical Philosophy," Philosophical Topics 19 (1991): 119-52. (112) See Watkins, "Kant's Theory of Physical Influx." (113) I should like to thank Roger Ariew, Martha Bolton, Jan Cover, Phillip Cummins, Marjorie Grene, Heiner Klemme, Sven Knebel, Manfred Kuehn, Mike Murray, and especially Karl Ameriks for their helpful comments on an earlier version of this paper. Also, I greatly benefited from discussion with the members of the Fall 1994 Midwest Seminar in the History of Early Modern Philosophy. Finally, I would like to acknowledge financial support from the Fulbright Commission and the Germanistic Society of America for the 1992-93 academic year, during which time I was able to pursue much of the research