To my friend who argued that Kant denied that we have any direct knowledge of the objective world and is therefore a relativist, I’ll give my take on Kant, and maybe one of my professional philosopher friends (at least one of whom I know is listening) can add his or her two cents.
My friend’s premise that Kant denied us any direct knowledge of the objective world is true. The conclusion, that Kant is a relativist, might then seem a no-brainer, but a close look shows that this conclusion does not follow from the premise.
Kant is indeed famous for subjectifying everything at the end of an eighteenth century which sought, through empiricism, to objectify everything. What is the most basic thing about the world as we know it? Space and time. Kant meticulously argues that space and time are not “out there,” not things in the world but ways of organizing the world. They are the subjective categories through which we make sense of the otherwise inaccessible flux of reality. But crucial is the idea that they are subjective categories and not objective facts. And if space and time are subjective categories, then it follows that everything we know about the world is subjectively constructed. Or, in Kantian terms, the world we know is the phenomenal world. It turns out that our knowledge presupposes a noumenal world anterior to the phenomenal world, but we have no access to such a world – it exists for us merely as an abstract, logical prerequisite.
This radical subjectification of the human experience would seem to throw us into a dizzying relativism, but not so in Kant. Indeed, Kant tells us in his early notebooks (before the Big Three critiques – of pure reason, of practical reason, of judgment) that his whole goal is to find universals in a world that seems to have spun off into relativism. It was David Hume who had carried empiricism to its logical conclusion, using the five senses to show that we have no evidence that external reality exists. Kant felt the justice of Hume’s argument, but like many was uncomfortable with the loss of all universal reference points. He felt that there is something universal about reality, that there is some shared universe we occupy. Kant’s epiphany came when he saw that if we were to have universals, we would have to locate them subjectively, not objectively. The objective world cannot give us universals because it is, insofar as we have access to it, always already shaped by subjective categories of understanding.
So how does Kant find a universal ground for ethics? I’m not sure because the Critique of Practical Reason is the one I’m least familiar with. But I can say how he does it in regard to aesthetics (the subject of the Critique of Judgment).
A true (valid) aesthetic judgment is (1) disinterested, (2) subjective, and (3) universal. Disinterested: “The satisfaction which we combine with the representation of the existence of the object is called ‘interest.’” I.e., if the satisfaction involves a vested interest in the existence of the object, it is an interested judgment. “You’re beautiful because our sex is great” is NOT a disinterested judgment: “A judgment about beauty in which the least interest mingles, is very partial and not a pure judgment of taste.” To be freed from such interest, a judgment must be subjective: “When the question is if a thing is beautiful, we do not … depend on the existence of the thing … but … judge it by mere observation … We wish only to know if this mere representation of the object is accompanied in me with satisfaction, however indifferent I may be as regards the existence of the object of this representation.” Only a subjective judgment is truly disinterested, and thus only a subjective judgment can be universal: “For the fact of which everyone is conscious, that the satisfaction is for him quite disinterested implies in his judgment a ground of satisfaction in all men.”
So to achieve an unbiased view, you must strip away all vested interest in the existence of objects at hand. Only then can your judgment be disinterested and therefore universally valid (and by definition, then, you are viewing it subjectively, as mere “representation” without regard to its objective existence).
I assume the analogy holds for ethics. An ethical judgment, to be valid, must be universal, and it can only be universal if disinterested, and only disinterested if subjective (stripped of all self-interest in the objective reality of the representation at hand).
What my friend who started this discussion wants, Kant would say, is not an objective ground of ethics per se; he wants a universal ground of ethics. And he would do best to find it subjectively, not objectively.