In this thesis, I compare Kant's and Wittgenstein’s takes on Transcendental Idealism, as a doctrine meant to “prove” the possibility of Metaphysics. My Central Question is: Is the early Wittgenstein a transcendental idealist? In virtue of a distinction between Transcendentalism and Transcendental Idealism, I answer “No”, by arguing that the early Wittgenstein is a transcendental philosopher, but not a transcendental idealist of any kind. In particular, I distinguish two variants of Transcendental Idealism, namely an effable variant, which Kant endorsed, and (...) an ineffable variant, often ascribed to Wittgenstein. And I argue that Wittgenstein cannot commit to either variant. This raises questions as to what kind of transcendental philosopher Wittgenstein is, if not an idealist one, and how his stance may bear on Metaphysics. I answer both questions by the end of the work. (shrink)