Re: The analytic-synthetic dichotomy and Kantian dualism between the noumenal and the phenomenal
his epistemology constitutes a novel attempt to intellectually justify that metaphysics by laying claim to possibilities of a priori knowledge, i.e. knowledge quite independent from experience
This is precisely the point I try to catch. To begin with, the contrary picture is not uncommon — that Kant's analytic/synthetic distinction is quite traditional (being a kind of reinterpretation of the classical distinction between necessity and contingency), whereas his metaphysical dualism between the noumenal and the phenomenal is quite new. I strongly disagree at least with the first assertion, but all this is just by the way. The main question is about the (inter)connection between the kinds of knowledge allegedly exempt from experience and the dualism at issue. It is quite clear that Kant's aim behind formulating the new logical dichotomy is to define a class of synthetic a priori truths. However, if we remember his main question — on how they are possible — we rather have to answer it in the following fashion: they are possible because all knowledge is about mere appearances, not vice versa. Therefore, given that the dualism in question constitutes the inherent part of the so-called Copernican turn, and synthetic a priori truths do not ground this dualism, it is not clear how the truths in question can ground the Copernican turn. But if they cannot do this, it is not clear what else can ensure this so-called turn and what does it consist in if it cannot justify the metaphysical dualism at issue.
The situation becomes more complicated if we consider those philosophers who accept the analytic/synthetic dichotomy but reject synthetic a priori judgments. Indeed, "positivists" should adhere to the Copernican turn since their theories depend on postulating the "subjective" character of linguistic conventions and meaning. This suggests that the turn at issue can be ensured merely by the so-called analytic truths. But this makes the situation even more mysterious — we are left with a plain circularity between the truths allegedly exempt from experience and the dualism between the noumenal and the phenomenal. And what could such philosophers say about the epistemological and ontological status of things-in-themselves?