 An essential aspect of all these arguments, according to Kant, is their attempt to derive conclusions about the nature and constitution of the “soul” a priori, simply from an analysis of the activity of thinking. A classic example of such an attempt is provided by Descartes, who deduced the substantiality of the self from the proposition (or, perhaps better, the activity) “I think.” This move is apparent in the Cartesian inference from “I think” to the claim that the “I” is therefore “a thing” that thinks. For Descartes, this move is unproblematic: thought is an attribute, and thus presupposes a substance in which it inheres. Kant emphasizes the a priori basis for the metaphysical doctrine of the soul by claiming that in rational psychology, the “I think” is supposed to provide the “sole text” (A343–4/B401–02). It is this feature of the discipline that serves to distinguish it from any empirical doctrine of the self (any empirical psychology), and which secures its status as a “metaphysics” that purports to provide synthetic a priori knowledge.