possibility which, because it is a priori in the most original sense, must obviously, already, and most originally reside in the mind. Knowledge, as we have seen, is comprised of the two stems (sensibility and understanding). But the understanding is the faculty of judging—i.e., the faculty of the function of unity. Ergo, the understanding is what we were looking for as this condition of the possibility of the unity of the given manifold. This is an extrinsic way of arguing the point.

Kant looks more precisely into the structure of the understanding itself. The understanding is certainly the “source of combining,” because a combination could never come about through the senses and also could never be contained even in the form of intuition. “All combining is . . . an action of the understanding” (B 130). Combining (synthesizing) entails a manifold, but not only that. Combining or relating requires a pre-view of the basis-on-which this can be combined with that. This “with” requires a “together,” the σύν requires a ἕν. Combining combines by way of a pre-view of unity. To combine is to unite, and in [321] all uniting, unity is already antecedently presented. Transcendental unity “alone is objectively valid” (B 140).

I call your attention to the connection of these observations with our earlier ones about Aristotle’s position on σύν and ἕν in relation to ὄν. We have now reached an area where the same issue is in play. Insofar as this unity in general makes possible combining and unification, it is a constitutive presupposition of every action of the understanding. Here again we meet the phenomenon of the pre-view, but we have to distinguish it from what we set out in the analysis of order. There it was a question of the pre-view of manifoldness as such, on the basis of which a given manifold gets understood. Here it is a question of a pre-view of a unity on the basis of which a manifold is to be combined as this specific manifold.

As regards its structure, combining is the presenting of a unity (qua basis-on-which) that enables the manifold be thought as a “one thing.” This synthesis-enabling unity is what Kant, in a striking turn of phrase, calls a “synthetic unity” (B 130).

The presentation of this unity cannot, therefore, arise from the combina-tion. Rather, by being added to the presentation of the manifold, it makes the notion of combination possible in the first place. (B 131)

Therefore, it is not the understanding as combining that constitutes that unity. Rather, the understanding [qua combining] has need of that unity. This unity must be able to be given as such if there is to be any understanding [qua combining] at all. Therefore Kant says that this unity “itself contains the basis . . . of the possibility of the understanding, even in its logical use” (B 131) of pure combining, where it is not