General Notion Of The Directing Principles Of Knowledge

The Philosophical System of Thomas Aquinas

Book by Maurice de Wulf (edited & adapted for the Web by Dr. Jonathan Dolhenty)

IV. The Directing Principles of Knowledge


  • A. General notion of the directing principles of knowledge
  • B. Origin and nature of these principles
  • C. Logical and real value

A. General notion of the directing principles of knowledge

Our knowledge consists of judgments, connected and coordinated with one another. The progressive life of the mind moves by a regular process in which judgments are built upon other judgments, so that the judgment is the principal and central act of the mind (II, D). Amongst these mental enunciations there are some which play a capital role in the life of the mind. They rule not only its psychological development, but also its epistemological and logical functioning, and therefore they deserve our special attention. We call them the directing principles of knowledge. To this class belong

  • the principle of contradiction (a thing cannot both be and not be);
  • the principle of identity (that which is, is; being is equal to itself);
  • the principle excluded middle (there is no middle term between being and non-being);
  • the principle of sufficient reason (being is endowed with all the elements without which it could not be);
  • the principle of totality (the whole is equal to the sum of its parts);
  • the principle of efficient causality (non-necessary being exists by the influence of a being other than itself).

There are many others. All form one long series, in close connection with the principle of contradiction, of which they all express different elementary phases or applications.

These judgments are called principles because they serve as a basis for other judgments:

  • first or immediate principles, because it is impossible to prove them by reference to more fundamental judgments;
  • directing principles (axioms or axiomata in the language of the Schoolmen) because they express simple relations between being, of whatever kind it may be, and certain elementary and primordial notions which are connected with being, such a ‘non-being,’ ‘whole,’ ‘part,’ ‘commencement of existence.’

B. Origin and nature of these principles

We may say that experience is the source of these principles, in the sense that the ideas which form the subject and predicates of the judgment are derived from experience. ‘Being,’ ‘whole,’ ‘commencement of existence,’ ‘causality,’ are derived from the matter of our internal and external sensations, by way of abstraction. We may go farther and say that experience facilitates the enunciation of the relation between the subject and predicate. For instance, I enunciate the principle of contradiction in realizing that I cannot be in the lecture hall and in the dark room at the same time; and the principle of causality, in realizing that my arm is raised by the command of my will acting as a cause.

But it is of vital importance to note that for the Schoolmen the bond of union established between the subject and predicate of the first principles we are considering is based, not upon experience, but upon the content of the subject and predicate, as revealed by mere analysis. When I say A = A, this judgment results from the mere consideration of A (whatever it may be) and not from experience. Since it does not depend upon human experience, which attains only to what actually exists, the bond of union expressed by these principles is therefore independent of the existence of the present universe, and, in fact, of all creation. Their validity does not depend on the condition that something exists: it is absolute. If the universe had never existed, and there was just one intelligence besides God, this would have been capable of knowing the axioms which govern human knowledge. The idea of being, and the other primordial notions correlative to it, could be obtained by such an intelligence from its knowledge of itself, or from God, and the juxtaposition of subject and predicate is sufficient to reveal the relation between them in the case of the axioms in question.

This supposition shows that there is no contradiction between the view expressed earlier that the constituent ideas of these principles (being, non-being, totality, etc.) are abstracted by the mind from external or internal sense perceptions, and this other view that the bond uniting these contents may be grasped without the aid of experience.

By reason of these characteristics, directing principles or axioms belong to a comprehensive class of judgments which are said to be ‘knowable as a result of the mere juxtaposition of the terms’ subject and predicate (propositio per se nota) and which would be called today judgments of the ideal order.

This class of judgments is opposed to a second category, which we need not study here, but which we mention only in order to emphasize the nature of the directing principles which we are now considering. In this second category of judgments, it no longer suffices to juxtapose the term in order to see the relation between them: we must have resource in addition to experience (propositio per aliud nota; the aliud is experience). If I do not need to subject my judgment to the control of experience in order to know that being and non-being are mutually exclusive, this control is indispensable in the case of the judgment that water boils at 100 degrees C.; or that men have a natural tendency to live in social groups. The second class of judgments would be known today as judgments of the existential order (XVI, B).

Let us consider more closely the group of judgments to which our directing principles belong. It would appear at first sight that the judgment of the ideal order of the Schoolmen coincides with the ‘judgment de jure‘ of Leibnitz, and the ‘analytic’ judgment of Kant, i.e., the judgment in which the subject includes the predicate. It is true that scholastic philosophy classifies among judgments of the ideal order these propositions, which Kant despised as mere tautologies. But Thomas Aquinas goes on to point out that there is another kind of judgments of the ideal order, knowable by the mere analysis of the subject and the predicate, and which is much more interesting. In these the predicate is not included in the subject, but nevertheless a clear knowledge or insight into the predicate reveals the bond which indissolubly unites it with the subject, once this subject is give. Although the predicate is not contained within the subject, there is an exigentia, or need, which imperiously demands the union of predicate and subject. The axioms which we are considering in this part all belong to this second class, except perhaps the principle of identity.

Take, for instance, the principles of contradiction and that of causality. The mere analysis of the notion of being will never reveal the notion of non-being (the negation is not implied in the affirmation), nor that of incompatibility with (the relation with is not implied in the notion of a thing considered in itself). But once the ideas of being and non-being are present to a mind the incompatibility of the two is forcibly evident. Or again, from the notion of ‘non-necessary existence’ we could never deduce that of ‘actual existence in the realm of fact.’ But if we juxtapose and compare the two notions, it is evident to us at once that the one is not the other, and that if a non-necessary thing is conceived as existing in point of fact we cannot explain this existence, without something other than itself. Indeed, a non-necessary thing is non-existent of itself. Hence, it cannot give to itself what it does not possess. As soon as this non-necessary being is represented as existing, it ought to be referred to some external influence — a causal influence — which is the sufficient reason of this existence. This is the enunciation of the principle of efficient causality: “The existence of a non-necessary being demands a cause.”

C. Logical and real value

Since the relation which unites the terms of the directing principles is so evident that ‘leaps to the eyes’ as the French say (sauter aux yeux), independently of experience, and since these principles express the laws of being as such and of all being, there will be no difficulty in allowing that they govern all conceivable being. They direct and control every assertion; they rule ‘universal intelligibility.’ They therefore rule and guide the collection of judgments which go to make up our human sciences, and likewise the various judgments which regulate our practical life. For instance, if the principle of contradiction were to become uncertain, or doubtful, no human affirmation would hold good, — not even the famous dictum, “I think, therefore I exist.” The assertion of my existence is not valid, if what I perceive as real can both be and not be. For this reason the principle of contradiction is called by the Schoolmen the first principle par excellence, and they make their own the declaration of Aristotle to the effect that a person who could not grasp this principle would not be a man, but a blockhead.

Do these principles, which apply to all conceivable beings, also govern existent being, in case anything is proved to exist? And if they govern the material universe as a whole, will they apply also to a world of suprasensible or spiritual beings, if such exist? These questions form part of the great epistemological problem which we must now consider.

Copyright © 1998 – 2012 Dr. Jonathan Dolhenty and The Radical Academy.

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.