  Kant then uses the claim that science proper requires the construction of the concept of the object in a priori intuition to exclude the possibility that chemistry and psychology, at least as they were practiced at that time, could count as science proper. In the case of chemistry, the problem is that “no law of the approach or withdrawal of the parts of matter can be specified according to which … their motions and all the consequences thereof can be made intuitive and presented a priori in space (a demand that will only with great difficulty ever be fulfilled)” (4:471). Since its principles are “merely empirical,” it can, at best, be a “systematic art” (ibid.). The case of psychology is more complex, since Kant provides (at least) two separate reasons in the Preface for denying it the status of natural science proper. First, Kant claims that mathematics is inapplicable to the phenomena of inner sense and their laws, though he grants that the law of continuity (discussed, e.g., at A207–209/B253–255 and A228–229/B281 in the Critique of Pure Reason) ought to apply to changes in our representations as well. He downplays the significance of this application of the law of continuity, however, by noting that time has only one dimension, which does not provide enough material to extend our cognition significantly. Second, Kant also complains that empirical psychology cannot separate and recombine the phenomena of inner sense at will; rather, our inner observations can be separated “only by mere division in thought” (4:471). Kant's fuller views on chemistry and psychology will be discussed further below.