This dissertation articulates and defends a new interpretation of the concept of mind which underlies Kant’s account of mental faculties in the three Critiques. On my reading, this concept is to be construed in terms of the transcendental idea of the soul (an immaterial thinking substance) in its regulative use. This offers an alternative to previous accounts, which construe Kant’s claims about the mind either as metaphysically neutral claims, as claims to cognition of the mind as an appearance, or as claims to cognition of the mind as a noumenal entity. On my reading, although Kant’s concept of mind is metaphysically substantive and even purports to give us a glimpse of noumenal reality, Kant’s use of this concept neither is grounded in cognitive access to an independently existing object nor gives rise to a claim to cognition of the mind as it is in itself. Rather, Kant’s employment of this concept in Critical philosophy is warranted by reason’s demand for explanatory understanding (or Begreifen), which cannot be fully met by our capacity for cognition.