11. The Abstract Character of Concepts Renders Judgment and Reasoning Possible. -- Every being which exists in nature is itself and no other, it is an incommunicable individuality, and it is inconceivable that one real being should be affirmed of another or attributed to another. Socrates is himself, he is no one else; this tree is this tree and no other.^{1}

How is it, then, that things are affirmed of one another in our judgments? It is because the mind has the power of looking at things without their individualizing notes: it abstracts.

In consequence of this abstractive mode of apprehension, the object of the concept is universal; that is to say, it is found, or can be found, in many other individuals, and can be attributed to them in our judgments (universale in praedicando).

Therefore, by means of intellectual abstraction, things can be affirmed, or, if we may so express it, are predicable, of one another. Thanks to this power of abstraction, our notions of beings as they are, are attributable to a whole species, a whole genus; in other words they reproduce characteristics of classes -- i. e., of genera and species. Abstraction makes reasoning possible; for reasoning, as we shall see later, supposes a universal middle term, and universality follows abstraction -- abstrahi ad quod sequitur intentio universalitatis.

{1} See General Metaphysics. "Particulars are not predicated of other [objects], but other [objects are predicated] of them." Aristotle, Prior Analytics, I, 27.