Abstract
The "theory already established" (CP 1.545) to which Peirce refers in the beginning of his 1867 paper "On a New List of Categories" has been almost unanimously identified with Kant's Transcendental Logic from his first Critique. While there is no doubt that this was, indeed, Peirce's own reference, the way in which he understood and used the Kantian framework has been subject to discussion from early on, and is still unsettled.
Instead of trying to offer an all-embracing interpretation of the problem, I will limit myself to the question how both Peirce and Kant understood the notion of "reducing the manifold". It will be shown that in rejecting Kant's proof of synthetic a priori judgments, Perice does not reject the idea of transcendental investigation (in terms of the conditions of possibility), nor does he limit himself to the explanation of analytic unity (as argues M.
Murphey 1961). In his pre-1867 semiotic, and especially its conception of interpretant as transcending and at the same time grounding the disctinction between synthetic and analytic reasoning, Peirce is able to prove the possibility and validity of inference in general and necessity of the categories, while on the other hand denying that any synthetic a priori judgment can be drawn from the consideration of its necessary conditions only.
This tentative concluding point bears much similarity to Apel's (1981) view of "semiotic transformation of transcendental philosophy", I would, however, like to show that it occured much earlier than Apel thinks, and interpret it in a rather different way regarding how "transcendental" is used by Kant, Apel, and Peirce.