In the Critique of Pure Reason, following his elucidation of the ‘postulates’ of possibility, actuality, and necessity, Kant makes a series of puzzling remarks. He seems to deny the somewhat metaphysically intuitive contention that the extension of possibility is greater than that of actuality, which, in turn, is greater than that of necessity. Further, he states that the actual adds nothing to the possible. This leads to the view, fairly common in the literature, that Kant holds that all modal categories, (...) in their empirical applications, are coextensive. I diverge from the common view. First, Kant is not committed to the coextensiveness thesis, understood as above. Instead, he espouses a weaker, epistemological version of the coextensiveness thesis, namely that what we can assert to be really possible is coextensive with what we cognize to be actual. Second, Kant's remarks are not intended to introduce a positive ontological thesis about the extensions of modal categories. Rather, he means to criticize a certain conception of modalities that was prevalent among his rationalist predecessors, i.e., the conception of modalities as various determinations that enter the intensions of concepts of things. (shrink)

Kant’s postulate of possibility states that possible is whatever agrees with the formal conditions of experience. As has often been noted, this is a definition of real possibility. However, little attention has been paid to the relation of Kantian real possibility to the German philosophical tradition before him. I discuss three kinds of possibility present in this tradition – internal, external, and (Crusian) real possibility – and argue that Kant endorses internal and external possibility. Furthermore, I show, specifically with respect (...) to the concept of state (Zustand), that the three traditional conceptions are reminiscent of three conceptions of real possibility that Kant implicitly distinguishes. Lastly, I argue that, according to Kant, we need experience to prove real possibility (at least as regards the three conceptions of the real possibility of states) because otherwise we could not know whether the formal conditions of experience obtain. (shrink)