In the Transcendental Dialectic of the first Critique, Kant famously claims that even if ideas and principles of reason cannot count as cognitions of objects, they can play a positive role when they are used “regulatively” with the aim of organizing our empirical cognitions. One issue is to understand what assuming “regulatively” means. What kind of attitude does this “assuming” imply? Another issue is to characterize the status of ideas and principles themselves. It is to this second issue that this (...) article is dedicated. Some interpreters have suggested that ideas and principles that can be assumed regulatively consist of propositions that we know are false. Others have suggested that at least some regulative ideas, as for example the idea of the homogeneity of nature, consist of propositions that we know are true but are indeterminate. Still others argue that, in assuming regulative ideas and principles, we assume propositions that cannot be proved true, but are nonetheless possibly true. In this article, I reject the view that regulative ideas consist of true but indeterminate propositions. Moreover, I argue that it is wrong to presuppose that only one of the remaining two options can apply to Kant’s account of regulative ideas and principles. By contrast, I submit that while in some cases assuming regulative ideas and principles does involve assuming some propositions that we know are false, this is not true for all regulative ideas and principles. More specifically, assuming regulative ideas involves assuming false propositions when assuming them means assuming that a “totality of appearances” is given. (shrink)