Thought, per se, is merely the purely spontaneous logical function which operates to connect the manifold of a possible intuition; and it does not represent the subject of consciousness as a phenomenon—for this reason alone, that it pays no attention to the question whether the mode of intuiting it is sensuous or intellectual. I therefore do not represent myself in thought either as I am, or as I appear to myself; I merely cogitate myself as an object in general, of the mode of intuiting which I make abstraction. When I represent myself as the subject of thought, or as the ground of thought, these modes of representation are not related to the categories of substance or of cause; for these are functions of thought applicable only to our sensuous intuition. The application of these categories to the Ego would, however, be necessary, if I wished to make myself an object of knowledge. But I wish to be conscious of myself only as thinking; in what mode my Self is given in intuition, I do not consider, and it may be that I, who think, am a phenomenon—although not in so far as I am a thinking being; but in the consciousness of myself in mere thought I am a being, though this consciousness does not present to me any property of this being as material for thought.
But the proposition, "I think," in so far as it declares, "I exist thinking," is not the mere representation of a logical function. It determines the subject (which is in this case an object also) in relation to existence; and it cannot be given without the aid of the internal sense, whose intuition presents to us an object, not as a thing in itself, but always as a phenomenon. In this proposition there is therefore something more to be found than the mere spontaneity of thought; there is also the receptivity of intuition, that is, my thought of myself applied to the empirical intuition of myself. Now, in this intuition the thinking self must seek the conditions of the employment of its logical functions as categories of substance, cause, and so forth; not merely for the purpose of distinguishing itself as an object in itself by means of the representation "I", but also for the purpose of determining the mode of its existence, that is, of cognizing itself as noumenon. But this is impossible, for the internal empirical intuition is sensuous, and presents us with nothing but phenomenal data, which do not assist the object of pure consciousness in its attempt to cognize itself as a separate existence, but are useful only as contributions to experience.
