The role of transcendental idealism in Kant's theory of knowledge has been both deliberately underrated and inadvertently exaggerated. If conceivably not necessary, its role in Kant's explanation of the possibility of a priori knowledge in the Critique of Pure Reason is at least pivotal to the success of the explanation. On the other hand, though transcendental idealism depends on Kant's epistemological criterion of an existing object, or, simply, his criterion of existence, the criterion for its part is actually independent of (...) the idealism. In fact, it may be because this independence has hardly been recognized that commentators have been unaware of the role the criterion may actually be playing in the continuing controversy over the correct interpretation of the idealism. Altogether, this article addresses both shortcomings – the underestimation and the exaggeration of the role of the idealism in Kant's epistemology. While it places the idealism at the centre of the epistemology, it also separates the criterion of existence from the idealism. In highlighting this contrast, the article explains how the criterion may actually be contributing to the persistence of the ongoing dispute over the correct interpretation of the idealism. (shrink)