Query: What famous philosopher was a transcendental idealist?
Context: Subjective idealists like George Berkeley are anti-realists in terms of a mind-independent world, whereas transcendental idealists like Immanuel Kant are strong skeptics of such a world, affirming epistemological and not metaphysical idealism. Thus Kant defines idealism as "the assertion that we can never be certain whether all of our putative outer experience is not mere imagining".