This paper reconsiders the relation between Kantian transcendental reflection (including transcendental idealism) and 20th century philosophy of science. As has been pointed out by Michael Friedman and others, the notion of a "relativized a priori" played a central role in Rudolf Carnap's, Hans Reichenbach's and other logical empiricists' thought. Thus, even though the logical empiricists dispensed with Kantian synthetic a priori judgments, they did maintain a crucial Kantian doctrine, viz., a distinction between the (transcendental) level of establishing norms for empirical (...) inquiry and the (empirical) level of norm-governed inquiry itself. Even though Thomas Kuhn's theory of scientific revolutions is often taken to be diametrically opposed to the received view of science inherited from logical empiricism, a version of this basically Kantian distinction is preserved in Kuhn's thought. In this respect, as Friedman has argued, Kuhn is closer to Carnap's theory of linguistic frameworks than, say, W.V. Quine's holistic naturalism. Kuhn, indeed, might be described as a "new Kant" in post-empiricist philosophy of science. This article examines, first, the relativization of the Kantian a priori in Reichenbach's work, arguing that while Reichenbach (after having given up his original Kantianism) criticized "transcendentalism", he nevertheless retained, in a reinterpreted form, a Kantian-like transcendental method, claiming that the task of philosophy (of science) is to discover and analyze the presuppositions underlying the applicability of conceptual systems. Then, some reflections on Kuhn's views on realism are offered, and it is suggested that Kuhn (as well as some other influential contributors to the realism debate, such as Hilary Putnam) can be reinterpreted as a (relativized, naturalized) Kantian transcendental idealist. Given the central importance of Kuhnian themes in contemporary philosophy of science, it is no exaggeration to claim that Kantian transcendental inquiry into the constitutive principles of empirical knowledge, and even transcendental idealism (as the framework for such inquiry), still have a crucial role to play in this field and deserve further scrutiny. (shrink)