Einstein envisioned a clear difference between a bottom-up physics that moves from observations to the conjecture of explanatory generalizations, and a topdown physics that deploys intuitively natural principles (especially of economy and elegance) to explain the observations. Einstein’s doubts regarding standard quantum mechanics thus did not simply lie in this theory’s use of probabilities. Rather, what he objected to was their status as merely phenomenological quantities configured to accommodate observation, and thereby lacking any basis of derivation from considerations of general principle.