If all C is D, then all A is B.
But, all C is D.
Therefore, all A is B.
Explain the difference between (1) the unity of the understanding which allows the concept A to be brought under the concept B and (2) the unity of reason which allows the judgment All A is B to be explained by the principle, If all C is D, then all A is B. In particular: both (1) and (2) involve the unification of the same manifold of possible cognitions: which ones? The purpose of the unification (1) is to “collect much possible knowledge into one” — that is, in this case, to allow the predicate concept, B, to be applied at once to every object of the subject concept, A. So the possible objects of A are to be united by virtue of their common conformity to the concept A. In virtue of what, and for what purpose, are the objects of A to be united in (2)?