摘要：Theories have traditionally been treated as axiomatic systems, consisting of a formally defined set of statements, the "fundamental laws" or the theory, closed under some, implication relation. The interpretation of the system comes only with the application of a selected subset of the terms, the : "observation vocabulary", to empirical or 0 bservahle: phenomena; in Ernst Nagel's words, "the fundamentel assumptions of· a theory constitute a set of abstract or uninterpreted postulates" (Nagel 1961, p. 91; cf.Carnap 1956). Explanation was correspondingly understood as deduction, or as Carl Hempel puts it, as "deductive BUbsumption under laws or theoretical principles" (1964, p. 291). In the familiar schematic form, explanation in the "Deductive-Nomological", (D-N) form, as elaborated by Hempel and Paul' Oppenheim, can be represented as follows:
