On the Practical Necessity of the Categories

Kant tells us that we cannot know whether all finite rational beings must share the same forms of sensibility. Can we know whether all finite rational beings must share the same forms of understanding? Recent discussion of this issue has focused on whether Kant thinks this can be decided from the theoretical point of view. But sometimes when knowledge gives out, we must have faith. Our concern in this essay is whether Kant thinks we can settle the question on distinctively practical grounds. We set out and evaluate an argument which would show that we have practical grounds to accept that all finite rational beings must share our forms of understanding. We consider ways in which this argument might be resisted and investigate the implications of the argument for the possibility of deciding the question on theoretical grounds. The connections Kant draws between morality, freedom, and causation show that any account of the kind of knowledge he thinks we can have of the forms of understanding of other finite rational beings must be part of a more general story about Kant’s account of the nature and limits of our knowledge of the moral law.