Aquinas: Intellectual knowledge: Idea, judgment, reasoning


The Philosophical System of Thomas Aquinas, by Maurice de Wulf, Edited & adapted for the Web by Dr. Jonathan Dolhenty

II. D. Several forms of intellectual knowledge: Idea, judgment, reasoning


Just as the sense knowledge of particular things has many forms, so also intellectual or abstract knowledge presents several stages — simple apprehension, judgment, and reasoning. They all are fundamentally abstract knowledge, i.e., an understanding of what something is, apart from the particularizing conditions in which it exists, or is capable of existing, outside the mind. Which are the psychological features of these three forms of thought?

In simple apprehension or concept or idea, the mind considers what a thing is, without affirming or denying anything about it. Example: triangle, square, whole, part.

The act of judgment consists in realizing that the content of two ideas — or two objects present to the mind — are in mutual agreement or disagreement. Example: the triangle is a surface; the triangle is not a sphere.

The abstract character which belongs to all our thoughts explains why the mind must make judgments, i.e., affirm this mutual agreement or disagreement. Why is it that we say, “the sum of the angles of a triangle is equal to two right angles,” “wine is changing into vinegar when exposed to the air”? Why are we not content simply to form the ideas ‘triangle’, ‘wine’? The answer lies in the richness of reality [10], and in the weakness of our minds. We are incapable of grasping by one single insight, or by one adequate intuition, all that there is in a real being. Only the penetrating eyes of God can exhaust the intelligibility of things by a single intuition, as Leibnitz says, and read in a blade of grass the network of relations which constitutes the history of the universe. Only God is able

To see a World in a grain of sand,
And a Heaven in a wild flower,
Hold Infinity in the palm of your hand,
And Eternity in an hour.

Our human mind, on the contrary, has to grasp reality piecemeal, and by partial aspects, or partial abstractions. We hunt and stalk reality, in the expressive language of the Schoolmen (venari), but never completely capture it. We discover in a triangle its properties and relations, we seize the activities, reactions of water. Then, after this mental dissection, we refer back to the thing we are studying — now become the subject of a judgment — each and all of the aspects discovered during our patient investigations. These several aspects correspond to several predicates of our judgments. Thus, we say S is P, “water freezes at 0 degrees C., it is composed of H2O, it boils at 100 degrees C., etc.” The mind unites things, after it has decomposed them, it makes a synthesis, and thus presents us with a complex object of knowledge. This explains why the notion which a chemist has of water is much richer in content than that of an ordinary person. Likewise, in a fragment of a Greek statue, the common man only knows superficial realities: marble, hardness, whiteness, etc., whilst the archaeologist places the whole statue in the history of art and as a part of an entire civilization. Judgment, then, which unites or separates (compositio, divisio are the scholastic terms), begins and ends with abstraction.

It follows from this that any of the aspects of an object (S) may become the predicate (P) of a judgment — not only those aspects which are qualities or attributes, but also activities displayed, state of existence, a relation, a situation in time or space. For example, the horse (S) is drawing a carriage, is sick, has more endurance than a mule, appeared in prehistoric time, in Northern Europe (P). Each of these aspects, which plays a part in making up the richness of the real object S is referred back to S by the mechanism of judgment through the of the copula is. The verb is does not indicate an inherence in the subject of any of those aspects, but the mental agreement of the subject and the predicate.

The same remarks apply to the process of reasoning, which is simple the production of a new judgment by means of two others, and whose final aim is to enrich the store of abstract knowledge about the special material (such as plants), human acts, numbers, etc.) upon which a special science turns its attention.


The late Dr. Jonathan Dolhenty was the Founder and President of The Center for Applied Philosophy and the Radical Academy, and is Honorary Philosophy Editor at The Moral Liberal. The Moral Liberal has adopted these projects beginning with a republishing and preserving of all of Dr. Dolhenty’s work.