To finish, let us return to the questions raised in chapter 3 about the coherence and defense of Kant's idealism. Since in section 4 of chapter 3 I discussed Kant's justification for the non-spatiotemporality thesis (NST) and the unknowability thesis (UT), here I shall focus on the consistency of his position. I shall not attempt to survey the literature, which is far too vast, nor to spell out in detail the prevailing interpretations. My bibliography contains enough references to point the reader in the right direction. Rather, my aim is to indicate briefly what I take to be the most charitable interpretation of Kant's position, expanding on my remarks on the B edition Preface in chapter 2.
Beginning with F. H. Jacobi in 1787, the most severe critics claimed that Kant is not justified in asserting that things in themselves exist, and that this claim, along with NST, violates UT. The merit of these charges, of course, depends on how one interprets the distinction between appearances and things in themselves. Historically, the two main contenders have been the “two worlds” and “double aspect” views. From Kant's time to the early twentieth century, commentators favored the “two worlds” view, according to which appearances and things in themselves are ontologically distinct. This view has generally lost ground, primarily because it is hard to support textually. If the two worlds are ontologically distinct, then it is difficult to understand in what sense appearances are of things in themselves, or how things in themselves could “ground” appearances.