Kant’s conception of the centrality of intellectual self-consciousness, or “pure apperception”, for scientiﬁc knowledge of nature is well known, if still obscure. Here I argue that, for Kant, at least one central role for such self-consciousness lies in the acquisition of the content of concepts central to metaphysical theorizing. I focus on one important concept, that of <substance>. I argue that, for Kant, the representational content of the concept <substance> depends not just on the capacity for apperception, but on the actual intellectual awareness of oneself in such apperception. I then defend this interpretation from a variety of objections.