 Kant’s criticisms of rational psychology draw on a number of distinct sources, one of which is the Kantian doctrine of apperception, or transcendental self-consciousness (often formulated in terms of the necessary possibility of attaching the “I think” to all my representations (B132)). Kant denies that the metaphysician is entitled to his substantive conclusions on the grounds that the activity of self-consciousness does not yield any object for thought. Nevertheless, reason is guided by its projecting and objectifying propensities. In accordance with these, self-consciousness is “hypostatized,” or objectified. Here again, Kant claims that a “natural illusion” compels us to take the apperceived unity of consciousness as an intuition of an object (A402). The ineliminably subjective nature of self-consciousness, and the elusiveness of the “I” in the context of that activity, are thus the well known bases for Kant’s response to rational psychology, and the doctrine of apperception plays an important role in Kant’s rejection. For in each case, Kant thinks that a feature of self-consciousness (the essentially subjectival, unitary and identical nature of the “I” of apperception) gets transmuted into a metaphysics of a self (as an object) that is ostensibly “known” through reason alone to be substantial, simple, identical, etc. This slide from the “I” of apperception to the constitution of an object (the soul) has received considerable attention in the secondary literature, and has fueled a great deal of attention to the Kantian theory of mind and mental activity.