 Kant’s view of space and time as exhibiting brute difference (i.e., the non-identity of locations in space and time cannot be reduced to conceptual explanation) stands in sharp contrast to the Principle of the Identity of Indiscernibles, and thereby also to the PSR. Salomon Maimon, Kant’s rationalist critic, attempted to enforce rationalist strictures on Kant’s philosophy by arguing that Kant is unable to explain the necessary agreement of intuitions and concepts. According to Kant, intuitions and concepts come from entirely different sources: sensibility and understanding. But if this were the case, claims Maimon, we could not explain the constant agreement between intuitions and concepts, which is necessary for the possibility of experience. This agreement can be explained if we reject the radical heterogeneity of intuitions and concepts, and view intuitions as disguised concepts. Thus, any difference exhibited in space and time must have its ground in the universal forms of our thought in general (Maimon, Essay on Transcendental Philosophy, Ch. 1, p. 13). Maimon also argued that we must seek an explanation for the fact that we have two forms of intuition rather than one, and suggested that it is only the interplay between the two forms of intuition which allows us to exhibit difference, by using a unity in one form to exhibit difference in the other form, i.e., conceive different times by concentrating on the change occurring at the same location in space, or conceive different locations in space at the same point in time (Essay, Ch. 1, pp. 13–14).