The answer to this is that in the case of contradictory statements - A and not A - the latter is a mere negation of the former, and posits nothing; and the negation of a notion with positive attributes, as the finite, does not extend beyond abolishing the given attributes as an object of thought.
The ego posits itself, but reflection on the given shows that we must add that it posits also the non-ego.
The method resembles that of the First Epistle of John, for although the errorists attacked in the latter manifesto are not those of the pastorals, and although the one writer eschews entirely the inner authority of the Spirit which the other posits, the same anti-gnostic emphasis on practical religion and stereotyped doctrine is felt in both.
According to him, the Ego posits first itself (thesis); secondly, the non-Ego, the other, opposite to itself (antithesis); and, thirdly, this non-Ego within itself (synthesis), so that all reality is in consciousness.
Hence it is the office of the theory of knowledge to show that the Ego posits the thing per se as only existing for itself, a noumenon in the sense of a product of its own thinking.