 The fact of science does not occur in the minds of individual scientists; it lies before us in books. “Experience” is not a representation in the mind of a knower; it is the objective content. “Experience” is virtually equated with mathematical natural science, and a paradigm “experience” is Newton’s law of universal gravitation. What makes experience (in this non-psychological sense) possible is “a priori”, now interpreted in a radically non-psychological sense as elements of the content of some aspect of culture that makes the objective validity of that culture possible. This new conception of the a priori, radically distinct from innateness and independent of any facts about human minds discoverable by empirical psychology, is articulated in Cohen’s Kant’s Theory of Experience. It is here that Cohen’s Neo-Kantianism breaks decisively with the Kantianism of Lange and Helmholtz. In his book, Cohen distinguishes between the “metaphysical a priori” and the “transcendental a priori” (1885: 109; cf. 1902: 44). The metaphysical a priori are the basic structures of our thinking that we can discover by introspection or empirical study; these are irrelevant to the transcendental philosopher (unless she is doing philosophy of psychology). The transcendental a priori, on the other hand, are those aspects of the content of science that make objective validity possible. Thus, the relationship between the a priori and experience is not like the relationship between a mental apparatus and its acts. It is a logical relationship, more like the relation between an axiom and a theorem (Cassirer 1918: 151, 153)—though with the important qualification that the a priori laws are not just axioms, but axioms that have the special semantic function of making objective validity possible.