Thank you both for your replies. I have to admit that I'm a bit puzzled by your responses. With regards to noumena, you both seem satisfied with Kant's treatment of them in the Critique. This seems to hinge on his "apophatic" approach, a kind-of "via negativa" that keeps Kant safe from contradiction.
While I don't deny that apophatic treatments have their place within philosophy (and perhaps theology), I'm not sure Kant's appeal works. This is because Kant is not simply denying
epistemic access to noumena, he's denying
conceptual access. Since all of our claims are mediated by concepts, and since concepts
cannot apply to noumena, the implication is that we should not even be capable of making claims about noumena, even just to say that they are the kinds of things about which claims cannot be made. Because in order to utter such a claim, we will have had to have conceptualized noumena, per impossible.
Kant cannot have it both ways. One the one hand he says:
For by no means do I require, nor am I warranted in requiring, cognition of this object of my idea as to what it might be in itself; for I have no concepts for that, and even the concepts of reality, substance, causality, indeed even necessity in existence, lose all meaning and are empty titles for concepts without any content when with them I venture outside the field of sense. — Critique of Pure Reason
And yet all of his talk about noumena necessarily employs concepts. When he claims that they exist, he applies the category of existence. When he claims that they are the cause of phenomena, he applies the category of causality. When he claims that they are not in space or time, he applies the category of negation. Even when he claims that the categories
cannot apply to noumena he applies the category of possibility and/or necessity!
The medievals ran into similar problems when making claims about God, but whereas they worked out sophisticated theories of analogy in order to deal with it, Kant hardly bothers to acknowledge that there's a problem. Kant's claim that we
must postulate noumena in order that our appearances be appearances
of something should have been a clue that he had made a false assumption somewhere along the way.
Again, I think this goes back to his faulty concept of representation/appearance. For what is the meaning of saying that we can know
only the appearances? How should we
know that they are appearances if we have no means of comparing them against what they are appearances of? The very concepts of appearance and representation seem to demand that we have some
positive conception of what it is that appears or what it is that is thereby represented.
Anyway, I apologize for the length of this post, but I really don't see how Kant's appeal to a "purely negative" conception of noumena saves him from contradiction, and I'm tempted to say that his concept of representation is downright incoherent, though I'm not as certain about that.
Now, you guys may say that I've still failed to convince, and that's fine. We can leave it at that.