Diana,

This is a great question, which touches what Kant perceived to be his greatest contribution to philosophy: to limit knowledge to save morality and religion. The answer took Kant two steps. Let me present them, stripped to the essentials and avoiding technicalities (we can always get back to this if you have further questions):

First, in the Critique of Pure Reason, Kant claims that our access to things is always mediated by the way we represent them. Things are not grasped immediately, but through basic cognitive structures inhering in the human mind. We cannot get rid of these structures, as we cannot get rid of our eyes and look at a world unadulterated by our mode of perceiving it. Thus, it is impossible to know how things are in themselves --all we know is how things appear to us, how we "see" them, so to speak. Furthermore, since the way things appear is not accidental, we can obtain knowledge of the world of appearances (the "phenomenal" world, as Kant calls it). This is why Kant believes he can justify the law of causality (determinism). This law, however, is circumscribed to appearances, and says nothing about how things might be as they are in themselves, i.e., in their non-humanly-mediated form of being. This form, of course, we cannot know --but we can nonetheless think of it, for there cannot be an appearance without something that appears (the thing in itself). Kant calls this realm "noumenal" and argues that we can conceive that freedom is possible in it, for causality only holds for phenomena. In short, the distinction between phenomena and noumena allows Kant to carve out a space for freedom, as it refers to things in themselves, and simultaneously preserve the truth of determinism, as it refers to appearances.

Now, this argument only proves the "possibility of freedom," not its reality. This is the job Kant reserves for himself in the second Critique. The second step, then, hangs on considering morality as a "fact of reason." Since morality requires freedom to be possible, and morality is something given to our reason as an undeniable fact, then freedom must be real.

Please let me know if you want me to delve into the more intricate details.

By: Pablo Muchnik at: 14th August, 2009