Is Kant’s Concept World Self-Contradictory?

Abstract There is a relatively overlooked problem with Kant’s claim that in inquiry we must treat nature as if it were actually infinite in extent: he also states that the concept of an actually infinite world is self-contradictory. This threatens to make the command to treat the world as infinite incoherent; the problem also affects his error theory for traditional metaphysics and his account of the sublime. After laying out this worry in greater detail than has been done so far, I consider and reject readings on which Kant either does not consider this case a violation of ought-implies-can or allows that in this case, following an incoherent demand is epistemically acceptable on consequentialist grounds. Then I turn to my preferred solution, which takes the relevant regulative principle to concern Kant’s noumena (understood as intensionally distinct from things in themselves), whereas the contradiction is provoked only by representations of phenomena.