St. Thomas Aquinas, the Catholic theologian and philosopher, was born at Roccasecca, Italy, the youngest son of Landolfo and Teodora of Aquino. At about the age of five he began his elementary studies under the Benedictine monks at nearby Montecassino. He went on to study liberal arts at the University of Naples.
It is probable that Thomas became a master in arts at Naples before entering the Order of Preachers (Dominicans) in 1244. He studied in the Dominican courses in philosophy and theology, first at Paris and, from 1248 on, under Albert the Great at Cologne.
In 1252 he was sent to the University of Paris for advanced study in theology; he lectured there as a bachelor in theology until 1256, when he was awarded the magistrate (doctorate) in theology. Accepted after some opposition from other professors as a fully accredited member of the theology faculty in 1257, Thomas continued to teach at Paris until 1259.
|University of Paris|
Thomas Aquinas then spent almost ten years at various Dominican monasteries in the vicinity of Rome, lecturing on theology and philosophy (including an extensive study of the major works of Aristotle) and performing various consultative and administrative functions in his order. In the fall of 1268 Aquinas returned for his second professorate in theology at the University of Paris.
He engaged in three distinct controversies: against a group of conservative theologians who were critical of his philosophic innovations; against certain radical advocates of Aristotelianism or Latin Averroism; and against some critics of the Dominicans and Franciscans and their right to teach at the university. Many of Aquinas’s literary works were in process or completed at this time.
It is thought that he was provided with secretarial help in this task, partly in view of the fact that his own handwriting was practically illegible. Called back to Italy in 1272, Aquinas taught for a little more than a year at the University of Naples and preached a notable series of vernacular sermons there.
Illness forced him to discontinue his teaching and writing toward the end of 1273. Early in 1274 he set out for Lyons, France, to attend a church council. His failing health interrupted the trip at a point not far from his birthplace, and he died at Fossanova in March of that year.
The writings of Thomas Aquinas were produced during his twenty years (1252–1273) as an active teacher. All in Latin, they consist of several large theological treatises, plus recorded disputations on theological and philosophical problems (the “Disputed Questions” and “Quodlibetal Questions”), commentaries on several books of the Bible, commentaries on twelve treatises of Aristotle, and commentaries on Boethius, the pseudoDionysius, and the anonymous Liber de Causis. There are also about forty miscellaneous notes, letters, sermons, and short treatises on philosophical and religious subjects.
Although Aquinas’s philosophic views may be found in almost all his writings (thus the “Exposition of the Book of Job” reads like a discussion among philosophers), certain treatises are of more obvious interest to philosophers. These are listed in detail at the end of this entry.
General Philosophical Position
|General Philosophical Position|
In the main, Aquinas’s philosophy is a rethinking of Aristotelianism, with significant influences from Stoicism, Neoplatonism, Augustinism, and Boethianism. It also reflects some of the thinking of the Greek commentators on Aristotle and of Cicero, Avicenna, Averroes, Solomon ben Judah ibn Gabirol, and Maimonides.
This may suggest that we are dealing with an eclectic philosophy, but actually Aquinas reworked the speculative and practical philosophies of his predecessors into a coherent view of the subject that shows the stamp of his own intelligence and, of course, the influence of his religious commitment.
One of the broad characteristics of Aquinas’s work in philosophy is a temperamental tendency to seek a middle way on questions that have been given a wide range of answers. This spirit of moderation is nowhere better illustrated than in his solution to the problem of universals.
|Solomon ben Judah ibn Gabirol|
For centuries philosophers had debated whether genera and species are realities in themselves (Plato, Boethius, William of Champeaux) or mere mental constructs (Roscelin, Peter Abelard).
What made this odd discussion important was the conviction (certainly shared by Aquinas) that these universals (such as humanity, justice, whiteness, dogness) are the primary objects of human understanding.
Most thinkers in the Middle Ages felt that if something is to be explained, it must be treated in universal terms. Therefore, the problem of universals was not simply an academic question.
Aquinas’s position on this problem is now called moderate realism. He denied that universals are existing realities (and frequently criticized Plato for having suggested that there is a world of intelligible Forms), but he also insisted that men’s universal concepts and judgments have some sort of foundation in extramental things. This basis for the universality, say of humanity, would consist in the real similarity found among all individual men.
It was not that Aquinas attributed an actual, existent universal nature to all individual men: that would be an extreme realism. Rather, only individuals exist; but the individuals of a given species or class resemble each other, and that is the basis for thinking of them as universally representative of a common nature.
Thomas’s spirit of compromise as a philosopher was balanced by another tendency, that toward innovation. His original Latin biographers all stress this feature of his work.
Thomas introduced new ways of reasoning about problems and new sources of information, and he handled his teaching in a new way. In this sense Thomas Aquinas was not typical of the thirteenth century and was perhaps in advance of his contemporaries.
Faith and Rational Knowledge
As Aquinas saw it, faith (fides) falls midway between opinion and scientific knowledge (scientia); it is more than opinion because it involves a firm assent to its object; and it is less than knowledge because it lacks vision.
Both are intellectual acts and habits of assent: in the case of faith a person is not sufficiently moved by the object to accept it as true, so, by an act of will, he inclines himself to believe.
|Faith and Rational Knowledge|
Knowledge implies assent motivated by a personal seeing of the object without any direct influence from will. Where objects of belief have to do with divine matters that exceed man’s natural cognitive capacity, the disposition to believe such articles of religious faith is regarded as a special gift from God.
Reason (ratio) is another type of intellectual activity: Simple understanding and reasoning differ only in the manner in which the intellect works. Through intellection (understanding) one knows simply by seeing what something means, while through reason one moves discursively from one item of knowledge to another.
Aquinas thought that philosophy entailed reasoning from prior knowledge, or present experience, to new knowledge (the way of discovery) and the rational verification of judgments by tracing them back to more simply known principles (the way of reduction).
Where the basic principles are grasped by man’s natural understanding of his sensory experiences, the reasoning processes are those of natural science and philosophy. If one starts to reason from judgments accepted on religious faith, then one is thinking as a theologian.
Questions V and VI of In Boethii de Trinitate develop Aquinas’s methodology of the philosophical sciences: philosophy of nature, mathematics, and metaphysics. He distinguished speculative or theoretical reasoning from the practical: The purpose of speculation is simply to know; the end of practical reasoning is to know how to act.
He described two kinds of theology: The philosophical “theology,” metaphysics, which treats divine matters as principles for the explanation of all things, and the theology taught in Scripture, which “studies divine things for their own sakes”.
Thus philosophy, for Aquinas, was a natural type of knowledge open to all men who wish to understand the meaning of their ordinary experiences. The “philosophers” whom he habitually cited were the classic Greek, Latin, Islamic, and Jewish sages.
Christian teachers mentioned by Aquinas were the “saints” (Augustine, John of Damascus, Gregory, Ambrose, Dionysius, Isidore, and Benedict); they were never called Christian philosophers.
The word theology was rarely used by Aquinas. In the first question of his Summa Theologiae he formally calls his subject sacred doctrine (sacra doctrina) and says that its principles, unlike those of philosophy, are various items of religious faith.
Thus, Thomas Aquinas was by profession a theologian, or better, a teacher of sacred doctrine who also studied and wrote about philosophy. He obviously used a good deal of pagan and non-Christian philosophy in all his writings.
His own understanding of these philosophies was influenced by his personal faith—as almost any man’s judgment is influenced by his stand for or against the claim of religious faith—in this sense Thomism is a “Christian philosophy.”
Aquinas did not ground his philosophical thinking on principles of religious belief, however, for this would have destroyed his distinction between philosophy and sacred doctrine, as presented in the opening chapters of the first book of Summa Contra Gentiles.
|A. E. Taylor|
One of the clearest efforts to maintain the autonomy of philosophy is found in Aquinas’s De Aeternitate Mundi (about 1270), in which he insists that, as far as philosophical considerations go, the universe might be eternal. As a Christian, he believed that it is not eternal.
Among interpreters of Aquinas there has been much debate whether his commentaries on Aristotle deal with his personal thinking. It is generally agreed even by nonThomists (W. D. Ross, A. E. Taylor) that these expositions are helpful to the reader who wishes to understand Aristotle. It is not so clear whether the mind of Aquinas is easily discernible in them.
One group of Thomists (Étienne Gilson, Joseph Owens, A. C. Pegis) stresses the more obviously personal writings (such as the two Summa’s) as bases for the interpretation of his thought; another school of interpretation (J.M. Ramírez, Charles De Koninck, J. A. Oesterle) uses the Aristotelian commentaries as the main sources for Aquinas’s philosophic thought.
|Charles De Koninck|
THEORY OF KNOWLEDGE. The Thomistic theory of knowledge is realistic. (This theory is presented in Summa Theologiae I, 79–85; Quaestiones Disputatae de Veritate I, II; In Libros Posteriorum Analyticorum I, 5; II, 20.) Men obtain their knowledge of reality from the initial data of sense experience.
Apart from supernatural experiences that some mystics may have, Thomas limited human cognition to sense perception and the intellectual understanding of it. Sense organs are stimulated by the colored, audible, odorous, gustatory, and tactile qualities of extramental bodies; and sensation is the vital response through man’s five external sense powers to such stimulation.
Aquinas assumed that one is cognitively aware of red flowers, noisy animals, cold air, and so on. Internal sensation (common, imaginative, memorative, and cogitative functions) works to perceive, retain, associate, and judge the various impressions (phantasms) through which things are directly known.
Man’s higher cognitive functions, those of understanding, judging, and reasoning, have as their objects the universal meanings that arise out of sense experience. Thus, one sees and remembers an individual apple on the level of sensation—but he judges it to be healthful because it contains vitamins, or for any other general reason, on the level of intellectual knowledge.
Universals (health, humanity, redness) are not taken as existing realities but are viewed as intelligibilities (rationes) with a basis in what is common to existents. As a moderate realist, Aquinas would resent being classified as a Platonist; yet he would defend the importance of our knowledge of the general and common characteristics of things.
Although human cognition begins with the knowing of bodily things, man can form some intellectual notions and judgments concerning immaterial beings: souls, angels, and God. Aquinas taught that man does this by negating certain aspects of bodies (for instance, a spirit does not occupy space) and by using analogy.
When the notion of power is attributed to God, its meaning is transferred from an initially physical concept to the analogous perfection of that which can accomplish results in the immaterial order. Thomas did not think that men, during earthly life, can know the nature of God in any adequate, positive way.
Discursive reasoning was taken as an intellectual process moving from or toward first principles in logical processes of demonstration (the ways of discovery and reduction, described above).
In one way, sense experience is the first principle (starting point) for all of man’s natural knowledge. This is one aspect of Aquinas’s empiricism. Following Aristotle’s Posterior Analytics, Thomas taught that many sensations combine to form a unified memory, and many memories constitute sense experience.
From this manifold of experience, by a sort of sensory induction, there arises within human awareness a beginning (principium) of understanding. Such first principles are not demonstrated (they naturally emerge from sense cognition), but they become the roots for consequent intellectual reasoning.
A doctor who tries a variety of remedies to treat headaches eventually notices that one drug works well in almost all cases—at some point he grasps the universal “Drug A is a general remedy for headache.” From this principle he proceeds rationally to order his practice. If he becomes a teacher of medicine, he uses such a theoretical principle to instruct others. This is the basis of the life of reason.
Philosophy and the Physical World
In his exposition of the Liber de Causis (Lect. 1), Aquinas described a sequence of philosophic studies: logic, mathematics, natural philosophy (physics), moral philosophy, and, finally, metaphysics.
|Philosophy and the Physical World|
The first kind of reality examined in this course would be that of the physical world. (At the start of the next century, John Duns Scotus criticized Thomas for attempting to base his metaphysics and his approaches to God on physics.)
Interpreters still debate whether Aquinas himself felt that this was the order to be followed in learning philosophy, or whether he was merely reporting one way that the “philosophers” had taught it. In any case, the philosophical study of bodies, of mobile being in the Aristotelian sense, was important to Aquinas.
One group of his writings (De Principiis Naturae, parts of Book II of the Summa Contra Gentiles, the treatise De Aeternitate Mundi) offers a quite personal treatment of this world of bodies. Another set of writings (the commentaries on Aristotle’s Physics and De Generatione et Corruptione) shows how indebted Aquinas was to Aristotle in his theory of physical reality.
|John Duns Scotus|
MATTER AND FORM. The philosophy of nature (phusis) was understood as the study of a special kind of beings, those subject to several kinds of change. Physical beings have primary matter as one component and, depending on their species or kind, substantial form as their other integral principle.
Neither matter nor form is a thing by itself; matter and form are simply the determinable and determining factors within any existing physical substance. Like Aristotle, Aquinas took it that there are many species of bodily substances: all the different kinds of inanimate material (wood, gold, water, etc.) and all the species of plants and animals.
Within each such species there is one specifying principle (the substantial form of wood, potato plant, or dog), and the many individual members of each species are differentiated by the fact that the matter constituting dog A could not also constitute dog B (so viewed, matter is said to be quantified, or marked by quantity).
CHANGE. Being mobile, physical beings are subject to four kinds of change (motus): of place (locomotion), of size (quantitative change), of color, shape, and so on (qualitative change), and of species of substance (generation and corruption, substantial change). Basically, prime matter is that which remains constant and provides continuity during a change from one substance to another.
When a pig eats an apple, that part of the apple really assimilated by the pig becomes the very substance of the pig; some factor in the apple, the prime matter,must continue on into the pig. All four types of change are explained in terms of the classic theory of four causes.
The final cause is the answer to the question “why” something exists or occurs; the agent or efficient cause is the maker or producer of the change; the material cause is that out of which the change comes; and the formal cause is the specifying factor in any event or existent. So used, “cause” has the broad meaning of raison d’être.
SPACE AND TIME. Certain other points in Aquinas’s philosophy of nature further illustrate the influence of Aristotle. Place, for instance, is defined as the “immobile limit of the containing body” (In IV Physicorum 6). Moreover, each primary type of body (the four elements still are earth, air, fire, and water) is thought to have its own “proper” place.
Thus, the place for fire is “up” and that for earth is “down.” Some sort of absolute, or box, theory of space may be presupposed; yet in the same passage Aquinas’s discussion of the place of a boat in a flowing river indicates a more sophisticated understanding of spatial relativity.
Time is defined, as in Aristotle, as the measure of motion in regard to “before” and “after.” Eternity is a type of duration differing from time in two ways: The eternal has neither beginning nor termination, and the eternal has no succession of instants but exists entirely at once (tota simul).
ENCOURAGEMENT OF SCIENCE. Doubtless Aquinas’s philosophy of the physical world was limited and even distorted by certain views and factual errors derived from Aristotle and from thirteenth-century science.
Apart from the mistaken hypothesis that each element has its proper place in the universe, Thomas also used the Eudoxian astronomy, which placed the earth at the center of a system of from 49 to 53 concentric spheres. (Besides the Commentary on De Caelo II, 10, and the Commentary on Meteorologia II, 10; see Summa Contra Gentiles I, 20, and Summa Theologiae I, 68, 4 c.)
At times Thomas showed an open mind on such questions and an ability to rise above the limitations of his period. His Commentary on Aristotle’s Metaphysics (Lect. 1 on Book III and Lect. 9 on Book XII) provides a key instance.
Pointing out that astronomers differ widely on the number and motions of the planets, Aquinas recommended that one study all the reports and theories of such scientists, even though these scientific explanations are not the last word on the matter and are obviously open to future revision.
He further compared the study of physical science to the work of a judge in a court of law. One should listen to, and try to evaluate, all important testimony before attempting to formulate one’s own judgment on the problems of contemporary science. This is Aquinas at his best, hardly a philosophical dogmatist.
Human Functions and man’s Nature
Anthropology, or psychology, in the classical sense of the study of man’s psyche, forms an important part of Aquinas’s philosophy. His view of man owed much to the Aristotelian treatise On the Soul, to the Christian Platonism of Augustine and John of Damascus, and to the Bible.
|Human Functions and man’s Nature|
This part of Aquinas’s thought will be found in Scriptum in IV Libros Sententiarum (Commentary on the Sentences) I, Dists. 16–27; Summa Contra Gentiles II, 58–90; Quaestio Disputata de Anima; the Libros de Anima; and Summa Theologiae, I, 75–90.
Aquinas’s usual way of working out his theory of human nature was first to examine certain activities in which man engages, then to reason to the kinds of operative powers needed to explain such actions, and finally to conclude to the sort of substantial nature that could be the subject of such powers.
He described the biological activities of man as those of growth, assimilation of food, and sexual reproduction. A higher set of activities included sensory perception, emotive responses to what is perceived, and locomotion: These activities man shares with brute animals.
A third group of activities comprises the cognitive functions of understanding, judging, and reasoning, as well as the corresponding appetitive functions of affective inclination toward or away from the objects of understanding.
To these various functions Aquinas assigned generic powers (operative potencies) of growth, reproduction, sensory cognition and appetition, physical locomotion, and intellectual cognition and appetition (will).
Reexamining these functional powers in detail, Aquinas distinguished five special sense powers for the cognition of physical individuals: sight, hearing, smell, taste, and touch. These functions and powers are called external because their proper objects are outside the mental awareness of the perceiver: This is essential to epistemological realism.
|John of Damascus|
Following these are four kinds of internal sensory activities: the perceptual grasping of a whole object (sensus communis), the simple retention of sensed images (imagination), the association of retained images with past time (sense memory), and concrete discrimination or judgment concerning individual things (cogitative sense, particular reason).
Still on the level of sensory experience, Aquinas (here influenced by John of Damascus) described two kinds of appetition (emotion): A simple tendency toward or away from what is sensed as good or evil (this affective power is called the concupiscible appetite), and a more complicated sensory inclination to meet bodily threats, obstacles, and dangers by attacking or avoiding them or by putting up with them (this affective power is called irascible appetite).
Eleven distinct kinds of sensory passions (emotions) are attributed to these two sensory appetites: love, desire, delight, hate, aversion, and sorrow to the concupiscible; fear, daring, hope, despair, and anger to the irascible.
Much of this psychological analysis is quite sophisticated, employing data from Greek, Roman, and early Christian thought and also using the physiological and psychological treatises of Islamic and Jewish scholars. It also forms the basis of the analysis of human conduct in Thomistic ethics.
On the higher level of distinctively human experience, Aquinas found various other activities and powers. These are described in his commentary on Book III of Aristotle’s De Anima, in the Summa Contra Gentiles (II, 59–78), and in Questions 84–85 of the Summa Theologiae. The general capacity to understand (intellectus) covers simple apprehension, judging, and reasoning.
The objects of intellection are universal aspects (rationes) of reality. Since universal objects do not exist in nature, Aquinas described one intellectual action as the abstraction of universal meanings (intentiones) from the individual presentations of sense experience.
This abstractive power is called agent intellect (intellectus agens). A second cognitive function on this level is the grasping (comprehensio) of these abstracted meanings in the very act of cognition; this activity is assigned to a different power, the possible intellect (intellectus possibilis).
Thus, there are two quite different “intellects” in Thomistic psychology: One abstracts, the other knows. No special power is required for intellectual memory; the retention of understandings is explained by habit formation in the possible intellect.
WILL. Affective responses to the universal objects of understanding are functions of intellectual appetition. Considered quite different from sensory appetition, this is the area of volition, and the special power involved is the will (voluntas).
Aquinas distinguished two kinds of volitional functions. First, there are those basic and natural tendencies of approval and affective approach to an object that is judged good or desirable without qualification.
In regard to justice, peace, or a perfectly good being, for instance, Aquinas felt that a person’s will would be naturally and necessarily attracted to such objects. This natural movement of the will is not free. Second, there are volitional movements toward or away from intellectually known objects that are judged as partly desirable or as partly undesirable.
Such movements of will are directed by intellectual judgments evaluating the objects. In this case volition is said to be “deliberated” (specified by intellectual considerations) and free. It is in the act of decision (arbitrium) that man is free.
Aquinas did not talk about “free will”; the term libera voluntas is found only twice in all his works, and then in a nontechnical usage; rather, he spoke of free choice or decision (liberum arbitrium). Man, by virtue of his intellectual powers, is free in some of his actions.
SOUL. Although Aquinas sometimes spoke as if these various “powers” of man were agents, he formally stressed the view that it is the whole man who is the human agent. A human being is an animated body in which the psychic principle (anima) is distinctive of the species and determines that the material is human.
In other words, man’s soul is his substantial form. Some of man’s activities are obviously very like those of brutes, but the intellectual and volitional functions transcend materiality by virtue of their universal and abstracted character.
Aquinas took as an indication of the immateriality of the human soul the fact that it can understand universal meanings and make free decisions. The soul is a real part of man and, being both immaterial and real, it is spiritual.
From certain other features of man’s higher activities, especially from the unity of conscious experience, Aquinas concluded to the simplicity and integration of man’s soul: It is not divisible into parts. This, in turn, led him to the conclusion that the soul is incapable of corruption (disintegration into parts) and thus is immortal.
Since Thomas thought the soul incapable of being partitioned, he could not explain the coming into being of new human souls by biological process. He was thus forced to the view that each rational soul is originated by divine creation from nothing.
Human parents are not the total cause of their offspring; they share the work of procreation with God. This view explains why Aquinas put so much stress on the dignity and sanctity of human reproduction, which he regarded as more than a biological function.
When he claimed, in his ethics, that the begetting and raising of children is the primary purpose of married life, he was not thinking of simple sexual activity but of a human participation in God’s creative function.
This does not mean that man is the highest of God’s creatures; Aquinas speculated that there are other kinds of purely intellectual beings with activities, powers, and natures superior to those of men.
These are angels. Thomas Aquinas is called the Angelic Doctor in Catholic tradition because of his great interest in these purely spiritual but finite beings. They would constitute the highest realm of the universe.
Metaphysics and Real Being
Aquinas devoted much thought to the question “What does it mean to be?” Many Thomists think that his greatest philosophical ability was shown in the area of metaphysics. His general theory of reality incorporates much of the metaphysics of Aristotle, and some interpreters have seen Thomistic metaphysics as but a baptized Aristotelianism.
Recent Thomistic scholarship has selected two non-Aristotelian metaphysical teachings for new emphasis: the theory of participation and the general influence of Platonic metaphysics (L. B. Geiger, Cornelio Fabro, R. J. Henle), and the primacy of esse, the fundamental act of being (Gilson, Jacques Maritain, G. P. Klubertanz).
|Metaphysics and Real Being|
Because esse, which simply means “to be,” is sometimes translated as “existence,” this second point of emphasis is called by some writers the existentialism of Thomistic metaphysics.
It has little, however, to do with present-day existentialism. A major treatment of metaphysical problems is to be found in Aquinas’s long Commentary on Aristotle’s Metaphysics, but here again the problem is to decide how much is Thomistic.
Some very competent scholars (Pegis, Gilson) regard this work as a restatement of Aristotelianism; others (De Koninck, Herman Reith) consider the Commentary to be a key exposition of Aquinas’s own metaphysics. It is admitted by all that there are some explanations in it that are not found in Aristotle.
Metaphysics, for Aquinas, was the effort to understand reality in general, to find an ultimate explanation of the manifold of experience in terms of the highest causes. His predecessors had variously described the subject matter of this study as existing immaterial substances, as the most universal and common aspects of being, as the first causes of all things, and as the divine being in itself.
Commenting on these opinions in the prologue to his Commentary on the Metaphysics, Aquinas remarked: “Although this science considers these items, it does not think of each of them as its subject; its subject is simply being in general.” In this sense, he called the study of being “first philosophy.”
ANALOGY. It is distinctive of Aquinas’s thought to maintain that all existing realities, from God down to the least perfect thing, are beings—and that “being” has in this usage an analogical and not a univocal meaning. In a famous passage (In I Sententiarum 19, 5, 2, ad 1)
Aquinas describes three sorts of analogy: one in which a given perfection is present in one item but only attributed to another; one in which one perfection exists in a somewhat different way in two or more items; and one in which some sort of remote resemblance or community is implied between two items which have no identity either in existence or in signification. “In this last way,” Aquinas adds “truth and goodness, and all things of this kind, are predicated analogously of God and creatures.”
In later works the notion of proportionality is introduced to develop the concept of the analogy of being. Vision in the eye is a good of the body in somewhat the same way that vision in the intellect is a good of the soul.
Similarly, the act of being in a stone is proportional to the act of being in a man, as the nature of a stone is proportional to the nature of man. Whereas some interpreters feel that the analogy of proportionality is the central type of analogy of being, others insist that Aquinas used several kinds of analogy in his metaphysics.
BEING AND ESSENCE. One early but certainly personal presentation of the metaphysics of Aquinas is to be found in the brief treatise De Ente et Essentia, which was strongly influenced by Avicenna.
His usage of basic terms of analysis, such as being (ens), essence (essentia), nature, quiddity, substance, accident, form, matter, genus, species, difference, immaterial substance (substantia separata), potency, and act, is clearly but rather statically defined in this opusculum.
Additional precisions, particularly on the meaning of element, principle, cause, and esse, are to be found in the companion treatise, De Principiis Naturae. A more dynamic approach to being and its operations is offered in the Quaestiones Disputatae de Potentia Dei and in Part I of the Summa Theologiae.
Fundamental in the metaphysical thinking of Aquinas is the difference between what a being is and the fact that it is. The first is a question of essence; the second is the act of being, esse. Essences are many (various kinds of things—stones, cows, air, men) and are known through simple understanding, without any necessity of adverting to their existence or nonexistence.
For a thing to be is entirely another matter; the fact that something exists is noted in human experience by an act of judgment. Many essences of things are material, but there is nothing about esse that requires it to be limited to materiality.
This proposition (to be is not necessarily to be material) is the “judgment of separation” (In Boethii de Trinitate V, 3). Many Thomists now regard it as a fundamental point of departure for Aquinas’s metaphysical thinking.
There are also certain most general features of real beings that transcend all division into genera and species; these are convertible with metaphysical being. In other words, they are coextensive and really identical with being. Such transcendentals are thing (res), something (aliquid), one, true, good, and (according to some interpreters) beautiful.
The more important of these transcendentals suggest that every being is internally undivided but externally distinct from all else (unum), that every being has some intelligible meaning (verum), and that every being is in some way desirable (bonum).
The theory of transcendentals is much more expanded and stressed in later scholasticism than in Aquinas’s own writings. He barely touches upon it in Questions I and XXI of De Veritate and in the discussion of God’s attributes in Summa Theologiae (I, Ques. 6, 11, 16).
POTENCY AND ACT. Potency and act are important principles in Aquinas’s metaphysical explanation of the existence and operation of things. In De Potentia Dei (I, 1) Aquinas pointed out that the name “act” first designated any activity or operation that occurs.
Corresponding to this sort of operational act is a dual meaning of potency (or power). Consider the activity of sawing wood: The passive potency of wood to be cut is required (water, for instance, cannot be sawed); also required is the active potency of the sawyer to do the cutting.
In addition, in the same text, Aquinas says that the notion of “act” is transferred to cover the existence of a being. Essential potency, the metaphysical capacity to exist, would correspond to this act of being (esse).
In this way the theory of act and potency was applied to all levels of being. At the highest level, God was described as Pure Act in the existential order, but this did not prevent Aquinas from attributing to God an active potency for operating.
FINALITY. Still another dimension of metaphysical reality, for Aquinas, was that of finality. He thought of all activities as directed toward some end or purpose, a basic assumption in Aristotle.
But Aquinas developed this tendential, vector characteristic of being and applied it to the inclination of possible beings to become actual. The finality of being, in Thomism, is that dynamic and ongoing inclination to be realized in their appropriate perfections that is characteristic of all realities and capacities for action.
In this sense the finality of being is an intrinsic perfectionism in the development of all beings. Aquinas also held that all finite beings and events are tending toward God as Final Cause. This is metaphysical finality in the sense of order to an external end. This theme runs through Book III of Summa Contra Gentiles.