ontological interpretation of subjectivity, the I, the ego, is for him, as it was for Descartes, res cogitans, res, something, that thinks, namely, something that represents, perceives, judges, agrees, disagrees, but also loves, hates, strives, and the like. Descartes calls all these modes of behavior cogitationes. The ego is something that has these cogitationes. But according to Descartes cogitare is always cogito me cogitare. Every act of representing is an "I represent," each judging an "I judge," each willing an "I will." The "I-think," "me-cogitare," is always co-represented even though it is not held in mind expressly and explicitly.
Kant adopts this definition of the ego as res cogitans in the sense of cogito me cogitare except that he formulates it in a more fundamental ontological way. He says the ego is that whose determinations are representations in the full sense of repraesentatio. We know that "determination" [Bestimmung] is not an arbitrary concept or term for Kant but the translation of the term determinatio or realitas. The ego is a res, whose realities are representations, cogitationes. As having these determinations the ego is res cogitans. Res must be taken to mean only what is meant by the rigorous ontological concept, namely, "something." However, in traditional ontology—we may recall Baumgarten's Metaphysics §36—these determinations, determinationes or realitates, are the notae or praedicata, the predicates of things. Representations are determinations of the ego, its predicates. In grammar and general logic, that which has predicates is called the subject. As res cogitans, the ego is a subject in the grammatical-logical sense; it has predicates. Subjectum is to be taken here as a formal-apophantic category. A category is called apophantic if it belongs to the structure of that which is the formal structure of the assertive content of an assertion in general. That about which the assertion is made, the about-which, is the subjectum, that which lies at the basis of the assertion. The asserted what is the predicate. The ego which has the determinations is, like every other something, a subjectum that has predicates. But how does this subject, as an ego, "have" its predicates, the representations? This res est cogitans; this something thinks, which means according to Descartes cogitat se cogitare. The thinker's being-thinking is co-thought in the thinking. The having of the determinations, the predicates, is a knowing of them. The ego as subject—taken throughout in the grammatically formal-apophantical sense—has its predicates in a cognizing way. In thinking, I know this thinking as my thinking. As this peculiar subject, I know about the predicates I have. I know myself. Because of this distinctive having of its predicates, this subject is a distinctive subject, that is to say, the ego is the subject κατ᾽ ἐξοχήν. The ego is a subject in the sense of self-consciousness. This subject not only is distinct from its predicates but also has them as known by it, which means as objects. This res cogitans, the something that thinks, is a subject of predicates and as such it is a subject for objects.