We now come to a conception which was not inserted in the general list of transcendental conceptions, and yet must be reckoned with them, but at the same time without in the least altering, or indicating a deficiency in that table. This is the conception, or, if the term is preferred, the judgement, “I think.” But it is readily perceived that this thought is as it were the vehicle of all conceptions in general, and consequently of transcendental conceptions also, and that it is therefore regarded as a transcendental conception, although it can have no peculiar claim to be so ranked, inasmuch as its only use is to indicate that all thought is accompanied by consciousness. At the same time, pure as this conception is from empirical content (impressions of the senses), it enables us to distinguish two different kinds of objects. “I,” as thinking, am an object of the internal sense, and am called soul. That which is an object of the external senses is called body. Thus the expression, “I,” as a thinking being, designates the object-matter of psychology, which may be called “the rational doctrine of the soul,” inasmuch as in this science I desire to know nothing of the soul but what, independently of all experience (which determines me in concreto), may be concluded from this conception “I,” in so far as it appears in all thought. Now, the rational doctrine of the soul is really an undertaking of this kind. For if the smallest empirical element of thought, if any particular perception of my internal state, were to be introduced among the grounds of cognition of this science, it would not be a rational, but an empirical doctrine of the soul. We have thus before us a pretended science, raised upon the single proposition, “I think,” whose foundation or want of foundation we may very properly, and agreeably with the nature of a transcendental philosophy, here examine. It ought not to be objected that in this proposition, which expresses the perception of one’s self, an internal experience is asserted, and that consequently the rational doctrine of the soul which is founded upon it, is not pure, but partly founded upon an empirical principle. For this internal perception is nothing more than the mere apperception, “I think,” which in fact renders all transcendental conceptions possible, in which we say, “I think substance, cause, etc.” For internal experience in general and its possibility, or perception in general, and its relation to other perceptions, unless some particular distinction or determination thereof is empirically given, cannot be regarded as empirical cognition, but as cognition of the empirical, and belongs to the investigation of the possibility of every experience, which is certainly transcendental. The smallest object of experience (for example, only pleasure or pain), that should be included in the general representation of self-consciousness, would immediately change the rational into an empirical psychology.