The second part of logic concerns the operation which either, on the one hand, composes or affirms one simple, singular concept with another, or, on the other hand, divides, separates, and denies one concept from another. This operation is traditionally calledJudgment.

The second act of the intellect combines or divides the simple objects that have been made known by the first act of the intellect. By the act of composition, we combine one simple object with another, as in ‘Man is artistic.’ By the act of division, we deny one simple object of another, as in ‘Wealth is not happiness.’ This composition and division of simple objects is not the mere juxtaposition of words, but an actual affirmation and denial.[1]

Propositions and Judgments

Propositions express these combinations (affirmations) and separations (denial) of simple concepts, and more than one basic logical propositions can be expressed in complex sentences. One should note that not all sentences are propositions, but only declarative sentences which affirm or deny a predicate of a subject (as opposed to questions, commands or requests, exhortations, and exclamations). Once we form positive propositions (affirmations) or negative ones (denials), we can make a judgment about whether the proposition obtains, i.e., conforms to the way things are in reality. In the intellect’s second act of composition or division, we must first form propositions in the mind before we can make a judgment about them.

Truth and Falsity

In a judgment, we assert that composition or division conforms to reality. If the composition or division conforms, the judgment is true; it is false if it does not conform. Thus, in hisCommentary on the Posterior Analytics of Aristotle which we cited above, Aquinas writes “The second operation of the intellect is composition or division, in which there is present the true or the false.” and reiterates the point inSumma Theologiae, I, q. 16, a. 1, “Truth is in the intellect [sc. judgment] composing and dividing.”

A judgment by our intellect presupposes that we have something to judge, namely, a composition or division of simple objects. We exercise judgment, then, on some composition or division of simple objects, and it is in this way that truth and falsity are in the second act of the intellect.[2]

Propositions express these judgments about things positively or negatively, universally or partially (as particular). Truth or falsity is first found in judgments, and there are interesting relationships between them according to whether they affirm or deny universally or partially, as we will see when we consider the Square of Opposition, below.

In the first act of the intellect, simple apprehension, there is neither truth nor falsity, just the consideration of a simple concept. Truth and falsity only apply to the mind’s acts of composition and division because truth is the conformity between what the mind considers in a proposition and the way the subject of that proposition is in reality, while falsity is the opposition between what the mind considers and the way it is. The word or concept “man” or “white” does not express anything about reality or any men that may or may not exist or anything that may or may not be white. “Man” is merely a concept, as is “phoenix” or “centaur” or “gold mountain.” These words or concepts do not express anything about how, or even if, any of them exist. How, or the mere fact that, they exist is something different from them as subjects that is added over and above what they are. (This is an important metaphysical point that Thomas discusses extensively inOn Being and Essence, which we will consider shortly.) But when the mind combines “man” with “runs,” it forms the proposition “The man runs” and asserts that something exists in a certain way. Or when the intellect separates real existence from the phoenix, it forms the propositions “Phoenixes do not exist.” Contrariwise, the mind may combine existence with centaur (which does not have it) and assert (falsely) “Centaurs do exist.” Only when the mind makes an actual assertion or denial, a judgment, about the way things are can there be conformity with reality, i.e. truth, or nonconformity, i.e., falsity. “The man runs” is true if it conforms to the reality of the man running, or it is false by not conforming when he is standing still. Because there are neither phoenixes nor centaurs in reality, the denial “phoenixes do not exist” is true, since it conforms to reality, but the assertion “centaurs exist” is false, because the assertion does not conform. In this way, Aristotle, and Aquinas after him, claim that only the second operation of the intellect, judgment, concerns the true and the false.

[1] John A. Oesterle,Logic: The Art of Defining and Reasoning (Prentice-Hall 1952), p.51.

[2]Ibid., p. 51.

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Updated January 18, 2025