POSSIBILITY

[A220/B268] Kant distinguishes real possibility, logical possibility, and formal possibility. [A218/B265] The postulate of possibility is "that which is agrees with the formal conditions of experience, that is, with the conditions of intuitions and of concepts, is possible". This is real possibility, which is narrower than strictly logical possibility (e.g., there is no logical contradiction "in the concept of a figure which is enclosed by two straight lines", although there is no real possibility of such a figure because it contradicts "the conditions of space and of its determinations"). [A127] Formal possibility is real possibility, or something quite similar (it may include only the conditions of the understanding), and it is connected with the doctrine of the Affinity. In the Deduction in A, Kant writes that "all appearances, as possible experiences...lie a priori in the understanding, and receive from it their formal possibility, just as, in so far as they are mere intuitions, they lie in the sensibility, and are, as regards their form, only possible through it".