The Metaphysics of St. Thomas Aquinas

All men naturally desire to know. — Aristotle.

[The following are excerpts from The Metaphysics of St. Thomas Aquinas, by Herman Reith C.S.C. University of Notre Dame (Bruce, Milwaukee 1958). This is an excellent book analyzing St.Thomas’ analyzation of Aristotle’s Metaphysics.]

A French philosopher of science, Emile Meyerson, once wrote: “Thinking metaphysically is as natural as breathing.” [De l’explication dans les sciences (Paris: 1927), p. 20] If, by “thinking metaphysically,” he meant, among other things, having a lively curiosity about ourselves and the world around us, wondering about such things as the origin and destiny of the world and of people in it, accepting, perhaps without knowing why, the first principles of reason that underlie our whole social structure—if that is what he meant, we would undoubtedly agree with his statement. What Meyerson said is more than a statement of a man who was himself a great thinker; it is something that everyone has experienced for himself at some time or another. Indeed, it would be more correct to say that this kind of thinking is more natural than breathing, because breathing is something shared with many other kinds of beings on earth, but thinking is something specifically human, and all thinking is to some extent metaphysical, since there are certain fundamental metaphysical presuppositions at the bottom of it.

If the statement about everyone being a metaphysician is true because in some way this simply means acting like a human being, then a broader statement that everyone is a philosopher is also true, for the metaphysician is the philosopher par excellence. Therefore, if we want to see more clearly how man is a metaphysician, we should first of all find out what the more generic classification, philosopher, means. Who is a philosopher? In his Commentary on the Metaphysics [of Aristotle] St. Thomas takes up the etymology of the word and tells us how it was first used:

“The philosophers were men who were moved to philosophize because of wonder, and since wonder comes from ignorance, it is evident that they began to philosophize in order to escape ignorance. So it is clear that they pursued knowledge and sought it zealously, only for the sake of knowing and not because of some utility.

“From the name wisdom that was first used (for this inquiry) there has been a change to the name philosophy, though both names mean the same thing. The early sophists who undertook the study of wisdom were called wise men. But when Pythagoras was asked what he would like to be called, he refused to take the name wise man, as his predecessors had done, because this seemed to him presumption. He called himself a philosopher, that is, a lover of wisdom. Hence the name was changed from wise man to philosopher, and from wisdom to philosophy. This latter name is more appropriate, for he is recognized as a lover of wisdom who seeks it not for the sake of something else but for itself. On the other hand, a person who seeks something for the sake of something else loves that for the sake of which he seeks something rather than what he seeks.” [St. Thomas, Commentary on the Metaphysics, I, 3, 55-56]

Chapter 1, The Need of Metaphysics

The Prescientific Metaphysics of Common Sense, continued

A philosopher is a person who wants to find an explanation of the things that he experiences—first of all in his own person and then in the world about him. He wants to understand for the sake of understanding; to him truth is its own reward. But he is a man who realizes that his intellect can never encompass the whole truth, the total explanation, and that is why he calls himself a lover of wisdom rather than a wise man. He realizes that what he discovers will never be a complete answer. Other men will come after him to add something significant to what he and others have said. They, too, will realize that the fullness of truth lies beyond them. They will see that wisdom can never be a personal possession: it can never be bought; it cannot be owned as one would own a house or automobile. Truth is by its nature independent of men’s minds, for it is divine, as even the “pagan” Greek philosophers knew.

Among the Greeks as among medieval philosophers it was the metaphysician more than anyone else who pursued knowledge for its own sake and for that reason was more deserving of the title philosopher. Most men pursue knowledge because of some other goal. Thus it would appear that metaphysical knowledge is a rare achievement, acquired only by the few. Yet, as we have seen, metaphysical thinking is natural for all men. How explain this seeming paradox?

It seems that there are several senses to the term metaphysics. In one sense it is knowledge that is almost synonymous with common sense, which itself has several meanings that can be applied in different ways to the kind of knowledge that Meyerson said is naturally found in man. Common sense can mean, first of all, the kind of knowledge that is contrasted with technical or scientific knowledge; it is the understanding that comes from the use of our native intelligence in the ordinary affairs of life. Common sense can also mean, in its more technical psychological context, the knowledge of the central sense (sensus communis), one of whose functions is to make us aware of the existence of sensible realities. Though this act of knowing cannot be called consciousness in the strict sense, it is at least a prereflexive consciousness that makes judgment and self-reflection possible. Through this power of the soul we are made aware of the activity of the physical world upon our sense faculties. But man cannot employ the various powers of his soul as though they could be isolated from each other. The unity of man is shown in the operations of any of his powers. Intelligence begins to operate as soon as the common or central sense makes us aware of the outside world. What man knows through his intelligence is not merely a sensation, but an embodied essence, an existing something. In this grasping of essence and existence in an object of sense experience man is first awakened intellectually and first begins to think metaphysically. At that moment the rudiments of the analogy of being that is at the heart of metaphysics are given. But this first judgment about reality is only the seed of metaphysics. Metaphysical truth has been planted in the soul; but, like seeds that are sowed by the farmer, some fall upon good ground and some do not; some begin to grow and then are destroyed by birds and drought; some continue to grow to mature life. St. Thomas says that this is the way it is with our knowledge of metaphysical principles:

“We must give a similar explanation of the acquisition of knowledge. For certain seeds of knowledge pre-exist in us, namely, the first concepts of understanding, which by the light of the agent intellect are immediately known through the species abstracted from sensible things. These are either complex, as axioms, or simple, as the notions of being, of the one, and so on, which the understanding grasps immediately. In those general principles, however, all the consequences are included as in certain seminal principles. When, therefore, the mind is led from these general notions to actual knowledge of the particular things, which it knew previously in general and, as it were, potentially, then one is said to acquire knowledge. “ [St. Thomas, Truth, 11, 1]

The prescientific metaphysics of common sense is sufficient for our ordinary intellectual needs. However, if some without formal training in metaphysics were to try to explain metaphysical principles to others, he would find that his knowledge is vague and that he does not understand the reasons for holding them. Thus metaphysical knowledge is paradoxical. It is the most commonplace insofar as its subject is found everywhere and its general principles are known by all men; but it is also the most difficult kind of human knowledge and therefore few men understand the significance of what they know. When the philosopher by profession investigates the principles and causes of being, he is working with a subject matter no different from that with which the ordinary man is acquainted. The fundamental truths of metaphysics are no different for the one than for the other. But to some extent it is the very proximity of the subject matter that makes metaphysical truths so hard for the untrained philosopher. In this domain we are, in the words of Aristotle, like bats that cannot see well during the brightness of the noonday sun; our minds are at home only in twilight reality. [Aristotle, Metaphysics, II, 1, 993b10] We cannot look directly at being and say what it is—we can see it better by looking out of the corner of our intellectual eye when we fix our attention more directly on something else immediately ahead.

Value of the Study of Metaphysics

St. Thomas has said in several places that one of the most important functions of the teacher is to point out at the beginning of any investigation the importance of the subject matter, because in this way he will make the student well disposed and eager to learn. [cf. Commentary on the Soul, I, 1, 2] In his Exposition of the Liber de Causis [preface] he does this by showing that the essential happiness of man will consist in the perfection of his intellect, and that the greatest natural happiness that a man can attain in this life will consist in the contemplation of the truths of metaphysics insofar as this leads to the knowledge of God. The fact that some people do not enjoy intellectual activity does not disprove his point, for men can be turned from their natural goal…

At the beginning of his Commentary on the Metaphysics, St. Thomas outlines the various kinds of knowledge that men pursue and then shows how, in this life, metaphysics is supreme among them. The first and lowest of all is that which man shares with irrational animals, namely sense knowledge…Beyond sense knowledge man has the knowledge of remembered experience…More perfect than this experience is his knowledge of how to make things—this is called Art. Art is primarily knowledge, not a manual skill. It is superior to experience because it deals more with the universal character of things and presupposes on the part of the artist a knowledge of causes, while experience remains a knowledge of contingent individual events. Mere knowledge of fact is not true understanding; consequently experience is not the kind of knowledge that is explanatory nor can it be taught.

Superior to art is scientific knowledge. St. Thomas advances several reasons to show why. First, a man of science is like an architect with respect to men in the building trades—he can give directions to others because he knows the reasons that are behind the arts and skills…His superiority comes, in the final analysis, because he knows the end that is to be achieved and the means of reaching it. Second, a man of science can teach others, whereas a man of experience can tell what happened to himself but cannot give precise instructions how anyone else should act…Third, a man of science can know some things with certitude, whereas the man of experience and the artist do not have absolutely universal norms of truth because they deal directly with singular, contingent things…

The metaphysician qualifies for the name man of science because these three characteristics are found in his knowledge of reality. But the metaphysician also differs from other men of science. For one thing, he arrives at many truths in a way that differs from the methods of other sciences. In addition, the truths he attains are more excellent than those investigated in other sciences. Some sciences prove the truth of a proposition by means of a demonstration from previous knowledge, as, for example, in geometry where a theorem is demonstrated from axioms that were previously seen to be true. But the basic truths of metaphysics are prior to and superior to truths that are demonstrated. If science through demonstration is valid, there must be universal and certain knowledge that is known without demonstration, otherwise the mind would require an infinite series of unsustained propositions. St. Thomas proves this point in his Commentary on the Posterior Analytics [I, 7]:

“Not all science is demonstrative, that is, acquired by demonstration. It should be understood here that Aristotle takes science broadly for any certain knowledge, and not as opposed to understanding, as when it is said that science deals with conclusions, but understanding with principles. That certain knowledge of some things is had without demonstration, he proves thus: It is necessary to know the prior things from which demonstration proceeds. At some point these must be reduced to things that are immediately certain. Otherwise it would be necessary to say that between two extremes, that is, the subject and predicate, there would be an infinite number of middle terms in act; even further, that there could be no two things between which there would not be an infinity of middles. In whatever way middles are taken, there must be something immediate to what follows. But since those which are immediate are prior, they must be indemonstrable. Therefore it is evident that knowledge of some things must be had without demonstration.”

Metaphysics is a Science

When we say that metaphysics is a science, we should not be misled into conceiving of it in the frame of reference of contemporary natural science, for the term science has a much broader scope. In its general sense the name is applicable to such diverse areas of knowledge as philosophy, logic, and mathematics, as well as to what we know as the empirical sciences. The contemporary notion of science usually implies the use of scientific method, in which mathematics play an essential role and in which the knowledge derived from the combination of observation and mathematical analysis passes through stages of hypothesis and theory, until it has been confirmed by subsequent experiments and generally accepted, when it is given the name of law. The immediate goal of empirical science is not the understanding of reality by means of ultimate causes but a reasonable explanation of the phenomena that can be observed in nature…Where the name is applied to metaphysics, as distinguished from the metaphysics of common sense, it means an understanding of the principles from which metaphysical truths can be drawn with certitude and necessity.

Metaphysics is Wisdom

Metaphysics is superior to other particular sciences because it is a wisdom and has a regulative or directive function in relation to the particular sciences. In the popular mind a wise person is more than someone who knows a great many things. The adjective “wise” has the connotation of knowing how to direct others wherever there is a common striving for a goal…With Aristotle, St. Thomas has set down the following characteristics of a wise man:

  1. He is one who knows all things at least in broad outline, though he may not know all things in the individual detail.
  2. He is one who understands difficult things over and beyond the ordinary understanding of men.
  3. He is one who has greater certitude than most men possess.
  4. He is one who better understands the causes of things.
  5. He is one who is more liberally educated, because he prizes knowledge as a goal in itself rather than as an instrument for something else.
  6. He is one who has greater dignity because he is able to direct others.

These are the characteristics that belong to the metaphysician and to the science of metaphysics…

Metaphysics is the basic directive science on the natural plane; it is the most certain of the sciences; it is the most universal of the sciences; it is the most liberal of the sciences.

Metaphysics is Directive Knowledge

“All sciences and arts are ordained to one thing, namely, the perfection of man, which is his beatitude. Hence, among them that one must be mistress of all the others which rightly lays claim to the title of wisdom. For it is the office of the wise man to order others.” [St. Thomas, Commentary of the Metaphysics, Preface]

If a number of things tend to the same general end, there must be some kind of order among them. This implies a principle of order, a principle of unity…Each thing operates and moves toward the end according to its own nature, it is true, but by the very fact that it is moving toward an end it participates in the perfection of the end. The causality of the end is found in different measure in all things that tend toward it; the end is the unifying principle…The diversity that is found among things in nature and in the arts and crafts is also found in the order of science. The ultimate goal of all science is the attainment of truth in its highest form; and this in turn will be the ultimate happiness of man…To act as an intermediary in the order of learning by which man achieves happiness is the role of metaphysics on the natural plan of human life, as it is of revealed theology on the supernatural plane of life.

As directive knowledge metaphysics is called First Philosophy. The name does not refer to the chronological order of learning, as we shall see, but to the priority that metaphysics enjoys with respect to other human sciences. Metaphysics has priority over other sciences because it, as the science of indemonstrable principles of being, is the guardian of the first principles of other sciences. In addition, metaphysics, as natural theology, is able to direct other sciences toward God, who is the origin and end of all things.

Metaphysics is Certain Knowledge

The certitude of other sciences could not be sustained without metaphysics, because the certitude of first principles is a presupposition in all the other sciences. The strength of a conclusion in mathematics, for example, can be no greater than the certitude of the principle of identity and of contradiction. But it is metaphysics that establishes the validity of the first principles. Since metaphysics does not go to any other science for its own principles but derives them by an analysis of its proper object, it is the foundation of the certitude of all other sciences that take these first principles for granted.

Metaphysics is Universal Knowledge

The need for a universal science is established on the grounds that there are genuine problems that lie beyond the scope of the particular sciences. In the context in which we speak, particular sciences are those that have limited subject matter and that demonstrate propositions through a restricted set of causes and principles…In one sense metaphysics is a particular science, in that it studies its subject in a way that is different from that of any other science, but it is at the same time a universal science because it treats of all being and because its principles and causes are applicable to all the other sciences.

Metaphysics is Liberal Knowledge

In brief, a man who is seeking knowledge for its own sake, as something in whose possession he can be happy, is on the way to being liberally educated. This purpose is contrasted with that inherent in the practical arts and practical sciences. They serve some more immediate goal, perhaps to produce what is necessary to sustain physical life, or to achieve some physical comfort over and above the necessities of life. Liberal knowledge is of the same essence of that spiritual quality by which a man has freedom. Liberal knowledge is spontaneous and unhampered by the dictates of a temporal pragmatic goal. All speculative sciences participate in this quality of freedom to a greater or less degree. Hence we can speak of pure mathematics, pure theoretical physics, or pure astronomy. But metaphysics is, among all kinds of human knowledge, the purest and most free.

What the ideal of the intellectual life shows is that it is not the immediately practical which is of paramount worth…It is only fitting that in the natural order of learning metaphysics should occupy us last, for it deals with that which, although most perfect in itself, is most difficult for us…Wisdom is knowledge sought pre-eminently for itself, and Aristotle, one of the greatest thinkers of the pre-Christian era, saw happiness as consisting principally in the contemplation of the objects of metaphysics. Not only was metaphysics conceived as the apex of the speculative sciences, it was also the reason for the practical sciences.

The Difficulty of Metaphysics

Philosophers have regarded the science of metaphysics as difficult to attain. Part of the difficulty comes from the lack of training regarding the subject matter itself, for it is not the kind of thing that can be seen immediately by the naked eye…This does not mean that someone cannot learn metaphysics if he is leading a very busy life, or if he is still a young person. But it does mean that one will not have the leisure or stamina to make the effort, or, if he is young, will probably get only a superficial understanding of metaphysical truths. That is why St. Thomas suggests that metaphysics should be studied after one has achieved a certain measure of leisure and maturity, and after one has become acquainted with other intellectual disciplines. Here St. Thomas speaks with the authority of one who is experienced in teaching a great number of young people:

“As far as wisdom is concerned, he [Aristotle] adds that young persons do not believe—that is, do not understand with their mind—the objects of wisdom or metaphysics, although they may speak them with their lips. But regarding mathematical entities, their essences are not hidden from them, because the definitions in mathematics concern things that are imaginable, whereas objects of metaphysics are purely intellectual. Now young people can easily grasp what falls under the imagination. But they cannot understand with their minds what transcends sense and imagination, because their intellects are not trained to such consideration owing to the shortness of their life and the many changes of their nature.

“Consequently, the fitting order of learning will be the following:

  1. Boys should be instructed in logic, because logic teaches the method of the whole of philosophy.
  2. They should be instructed in mathematics, which does not require experience and does not transcend the imagination.
  3. They should learn the natural sciences, which although not transcending sense and imagination, nevertheless require experience.
  4. They should be instructed in the moral sciences, which require experience and a soul free from passion.
  5. They should learn metaphysics and divine science, which transcend the imagination and demand a robust intellect.

Apart from the demands of the order of the subject matter, there is an important pedagogical reason for delaying the study of metaphysics until some familiarity is had with other parts of philosophy. Metaphysics is too difficult for a beginner, because it is too far removed from the kind of thinking that a young person is accustomed to. The natural order of the mind is to go from concrete sense experience to more abstract thinking. Like all natural capacities, the intellect moves slowly from potency to act. Therefore, metaphysics, which treats of beings furthest removed from matter, should come last in the chronological order of natural learning even though it is first in the order of dignity.


All things are good and are brought together in God who is the Origin and End of all…God is the absolute good who draws all things to Himself. It is on this note that St. Thomas ends his Commentary on the Metaphysics, namely that God is the Ruler of the universe, the source of unity in all things, the good that all things seek.

“Therefore we conclude that the whole universe is like one people and one kingdom, in which there must be one ruler who directs all who are in it. This is the conclusion that he [Aristotle] comes to, that there is one Lord of the whole universe, namely the first Mover, the first Truth, and the first Good, whom we have called God. May He be blessed throughout all ages. Amen.” [St. Thomas, Commentary on the Metaphysics, XII, 1, 2663]

The Metaphysics of St. Thomas Aquinas, by Herman Reith C.S.C. University of Notre Dame (Bruce, Milwaukee 1958)