Thomas Aquinas (1225-74) was born of a noble family at Roccasecca, Italy. From the age of five he began studying at the Benedictine abbey of Monte Cassino. In 1239 he went on to the University of Naples, where he studied the seven liberal arts of grammar, logic , rhetoric, arithmetic, geometry, music, and astronomy; while at Naples he entered the Dominican Order. His entry into this Order, with its emphasis on poverty and evangelism, was opposed by his family to such an extent that he felt the need to escape to Paris; but while on the road to Paris, he was abducted by his elder brother and locked up in the family castle at Monte San Giovanni . He was later held prisoner in Roccasecca for over a year. His family was unable either to strip him literally of hi s Dominican robes, or to persuade him to renounce the Order. While he was imprisoned hi s brothers sent him a seductress; but he drove her from the room with a burning brand, and the event merely reinforced his commitment to chastity. Eventually hi s family relented an d he returned to the Dominican Order, first at the University of Paris in 1248, then at Cologne under Albert the Great. During this time he became deeply versed in the works of Aristotle.
He returned to Paris in 1252 for advanced study, and he lectured there in theology until 1259. The next ten years of hi s life were spent at various Dominican monasteries near Rome; in 1268 he returned to teach again at the University of Paris. In 1272 he went to teach at the University of Naples; but ill-health forced him to stop work. In 1273 he had a mystical vision which caused him to regard hi s intellectual work as worthless-he consequently ceased work on the massive Summa theologica. In 1274 he was journeying to Lyon for a meeting of the church council, but had to rest at Fossanova, not far from his place of birth, owing to illness; there he died in 1274.
Aquinas’ character seems to have been one of imperturbability, and there is no doubting his sharpness of intellect. After his death the teaching of Aquinas and Thomism formed the official doctrine of the Dominicans, and this was adopted by some other Orders, but it was in general relatively neglected by the Catholic Church. However, in the nineteenth century Aquinas was commended by Pope Pius IX as the premier figure of Catholic philosophy and theology.
Aquinas’ thought owes a great deal to Aristotle, and he attempts to reconcile the central tenets of Aristotelian philosophy with Christian dogma; these attempts deal with issues like the nature of God, our means to salvation, and our understanding of the nature of creation. Aquinas’ thought begins with the presupposition that the universe is, at least partly, intelligible to finite human intellects: the structures and laws of the universe can be understood.
Aquinas hatches a compromise between the conclusions derived from our natural cognitive faculties (the senses and reason of secular philosophy), and conclusions derived from divine revelation (the faith of divine theology). One could dismiss one or the other as worthless, or say that each one ultimately depends on the other, as Augustine does; Aquinas however maintains the distinction, and says that they are two generally autonomous ways of looking at the same object, namely God. Whereas our natural cognition works “from below” to know God through His effects as the creator of the world, divine revelation-supernatural cognition-works “from above” to know God as cause. Thus faith (fides) and scientific knowledge (scieniia) are sharply distinguished not by object, but by method. Both are cognitive processes involving the assent of the intellect to truths; but whereas faith requires the addition of the will in order to believe truths with certainty, scientific knowledge requires no such application of will since the intellect either intuitively “sees” truths immediately, or argues validly to establish truths from intuitively known premises.
Within theology we can make a distinction between supernatural and natural theology: respectively, truths revealed about God and other elements of Christian doctrine which depend on divine revelation (grace, which derives from the Latin gratia, meaning favour), and those that can be known through natural powers of cognition. There is also an overlap of truths: some truths are both revealed and known through being provable by natural cognition. In this sense natural theology is part of supernatural theology. So the totality of truths grasped by the human mind has three parts.
(A) That which is believed only in virtue of divine illumination or revelation.
(B) That which is believed by divine revelation and is known by being provable by natural cognition.
(C) That which is known by natural cognition. Ideally a conflict will never arise between the deliverances of the revelations of faith, and the proofs of natural reason; but in the latter we are fallible, and a conclusion derived from reasoning that conflicts irreconcilably with a properly understood truth of faith shows that we have made a mistake in our reasoning. But we have, ideally, a twofold route to some Christian truths.
Natural cognition is made up of the senses and the intellect, and of these the senses are primary both genetically and logically for knowledge of existing things and for possession of abstract ideas; all the materials of our intellectual faculty-our ideas-are abstracted ultimately from the senses. The intellect is involved in forming judgements about what we perceive: that what we perceive really exists, that it has certain properties and that it is a certain kind of thing. The intellect also engages in abstract reasoning. The senses see X; the intellect actively judges X as X; the intellect goes on to understand and think of X when it is not perceived. The intellect goes beyond the sensory experience in forming a judgement, which is an affirmation or denial of some truth; this goes beyond the mere fact of one’s having a certain experience. The sensible aspects of particular things (red, sweet, warm, etc.) are given through sense-perception alone; but the intelligible aspects of particular things (that they exist, that they actually have certain properties and are certain kinds of things) are derived not from the passive association of the ideas of senses alone, but in conjunction with an active synthesizing and interpretative intellect, which forms from the ideas of sense complex conceptions and hypotheses. The intellect forms concepts-universal ideas-of things by abstracting general ideas from sense-experience; the intellect thinks of the nature of those things and how they are connected to other things by understanding those general concepts.
Aquinas follows Aristotle closely in not supposing that essences (the “whatness” of things) can exist apart from individual things; philosophically speaking, there is no universale ante rem, that is, essence before or apart from individual things; rather, essence is universale in re, present in individual things, in the sense that real things are real substances and are always compounded of two elements.
(a) Essence (esseniia, quidditas, natura). This is “whatness”; viewed epistemologically through a definition it tells us what a thing is .
(b) Existence (esse, which is a form of the Latin verb “to be”; but esse is also used as a noun). This is the fact that a thing is .
The difference between a mere essence (quidditas) and real substance is existence (esse); existence is what turns, by being “added” to it, a merely potential essence into an actual individual substance. This is the primary move from potentiality to actuality: mere potential existence to actual existence. Once a certain essence is actualized, there is a further process of change from potential to actualization as the essence brought into existence strives to fulfil its potential within its kind; an acorn (an actual acorn, but potential tree) will grow into a tree (an actual tree) . The terms above in (a) and (b) roughly correlate with the following.
(a’) potential (potentia, potency)
(b’) actuality (actus, act).
The difference between essence and potentiality is partly one of generality; to speak of essence is to imply some determinate potentiality: a certain “so-and-so”; whereas to speak of potentiality is to suggest mere possibility: some “so-and-so” or other. Anything that is not logically impossible has potentiality in the second sense.
To know the essence of something is to know its real definition, the essential features without which a thing would cease to be the kind or sort of thing it is. The accidental features that an individual kind of thing ha s are those features which it can lose or gain while remaining the same kind of thing. It is most important to note that Aquinas thinks that in giving a definition of the essential nature of an individual, he is giving a real definition; that is, the definitions are not a function of the way we conceptually happen to divide up the world, rather the definitions, if true, reflect accurately the way the world divides itself up. The distinction between essence and existence is also a real distinction. That is not to say we ever encounter in the world pure existence or pure essence, but the distinction is real in the sense of being independent of human cognition; it is not a distinction projected onto the world by the mind. For to say what something is is one thing, but to say that it is, is another; we can know what a dog is-the essence “dogness”-without committing ourselves to affirming either the existence or non-existence of dogs. Another way of putting thi s is to say that essences have no existential import. This is true for all entities except God; He alone has existence as part of His essence. For all other beings, existence (esse) is something added to essence-added to a mere determinate potentiality-by God; thus a ll things depend ultimately on God. Essence an d existence are never found in separation; nothing simply is, a thing always is a determinate kind of thing; to be is to be a “so-and-so” ; to be is always a determinate way of being. The obvious limitation of individual substances is explained by essences receiving esse and at the same time limiting that esse to a certain way of being. In God the esse is unlimited, and also eternal; there are no limits to God’s being; He has “fullness of being”.
For Aquinas as a Christian, unlike for Aristotle, the existence of things cannot be taken for granted but requires explanation. Aristotle thought that the world exist s eternally, and that any change in the world is not a change from ab solute non-existence (nothing) to absolute existence or vice versa, but a change either of an accident, or from one form of substantial being to another. For example a substantial change occurs when a tree ceases to be a tree and becomes ash when it is burnt. For Aquinas the very fact of existence itself is a problem; given that nothing, except God, has existence as part of its essence, an explanation beyond the essences of things is required to explain why anything is at all; that explanation derives from God the creator who adds esse to essences.
Apart from God, no essence is fully actualized. In God’s case, the positive essence is full y actualized. God does not merely actualize His divine essence; He actualizes it all the way, so to speak. If we take any other entity, we will always have an entity which ha s potential within its kind-its essence will not be fully actualized; there will be aspects of its essence th at it does not fully exemplify. God’s absolute perfection is to be identified with Hi s complete actualization of His positive divine essence-He is pure act (actus purus); He contains no unactualized potential of His positive divine essence.
The relation between essence and existence, and between potency and actuality, applies to any substance whatsoever. It must not be supposed that all real substances must be material or corporeal; not only material things have esse. The analysis of material things introduces another pair of terms, (i) form (morphe) (ii) matter (hyle).
This gives a hylemorphic theory of material substance. In the case of material substances, potential corresponds to matter; the matter is potentially a “so-an d-so”, and is actualized as an individual separable thing of a certain kind by taking on a certain form; that form is actualized in that matter. However, pure matter (materia prima) would be completely ineffable; it would by definition possess no character, no whatness. Only by the addition of form in act in the matter does it become a determinate “so-and-so”; matter as a mere determinable is not possible, although we can understand what we mean when we talk of it. The notion of pure potentiality as pure matter is impossible as something that exists-it would indeed be a contradiction-but it is intelligible conceptually. Indeed, pure potentiality cannot in any case exist. The soul is the form of human beings; and souls are individuated by the matter of the body of which they are the soul. But pure forms can exist , as well as material substances, when certain non-material essences receive esse. What Aquinas has in mind here seems to be a three-level hierarchy of being.
(1) Corporeal substances. These are matter and form; they are perishable and finite.
(2) Incorporeal limited substances. These are pure form-spiritual entities, which although imperishable are finite . The kinds of entities Aquinas has in mind here are the separated soul and angels.
(3) Incorporeal unlimited substance. This is pure act; all aspects of the positive essence receive existence (esse) . This is, in fact, God who alone exists necessarily, since in Him alone His way of being must be conceived as including existence; in Him no distinction can be made between the essence He has and His existence, for He necessarily completely actualizes His essence, all the positive aspects of the divine essence there are; there is nothing He is only potentially; there is nothing divinely positive He is not.
The object of human knowledge in intellectual cognition is the discovery of what essence is actualized in any individual. We understand substances in so far as we come to know the essence that is in act-is esse-in substances. Aquinas holds that for each known truth there must always be something existing (esse) that corresponds to that truth. Individual substances are understood by us not as individuals qua individuals (individual things as such: features which constitute their particularity), but through knowing that which is general or common in them that defines the nature of the kind in which all the individuals of a certain kind share. Thus we know a dog in so far as we know the real definition of “dog”, and hence understand it in its essential dogness; we do not know the dog in its full particularity because the terms we apply always have some generality of application.
An essence is what must be the case for a thing to be what it is: that which a thing cannot lack and still be what it is. Thus understanding what a thing is-its essence-is logically independent of the fact that a thing is, its existence. I can understand what a dog or a Phoenix is independently of whether it is . The essence of X is given in a set of necessary and sufficient conditions a, b, c for X to be the kind of thing it is . In this way we can form a real definition: X is of a specific kind if, and only if, a, b, c are true of X. When we are correctly said to know X, the aspect of X we know is that set of features X has in common with all and only other Xs of the same kind. We would not understand a clock as a clock by referring to its colour or the scratch on the face, but in so far as we understand that in virtue of which a clock is a clock: what makes it distinctively a clock and not another kind of thing. We understand the nature of the clock by understanding those common features shared by all and only clocks which define them as clocks. Then what makes a clock or a dog a particular clock or dog cannot be its essence or form, since that is common to all instances of the same kind, but must, Aquinas argues, be its being formed of a quantitatively or numerically different parcel of matter.
With incorporeal or spiritual substances such a method of individuation is clearly inapplicable; he suggests that each incorporeal substance must be individuated by essence; that is, the essence of each soul or angel must be different, so each angel differs in essence as a dog does from a cat; each angel is of a different, and unique, kind.
Aquinas strikes a middle course on the question of the reality of universals. Universals are general concepts or categories with which we talk about the world and with which we classify particulars into kinds or sorts. Aquinas adopts a form of moderate realism. He rejects the full realism of Plato, whereby universals exist as real entities in a world of intelligible Forms independently of the world of sensible things. He also rejects conventionalism, whereby universal concepts are mere arbitrary, subjective mental constructs, for which the most that can perhaps be said is that they are made for our convenience. Aquinas compromises: universals are objective in being real, extramental and immutable, but they exist in instances of individual kinds of things and cannot exist apart from those instances. Universals or kinds as such exist only in virtue of there being individual actual instances of those kinds. Only individuals exist, but the natures of those individuals radically resemble each other and are understood from this essential common resembling nature as being members of universal classes or species-for example, humanity, dogness, justice. Individual material things of the same kind are the same kind in virtue of sharing a substantial form; but that substantial form, although it cannot exist apart from the individuals who share it, is nevertheless something objective in the world, and derives its objectivity from the really existing common nature shared by individuals of the same class. The world divides itself into kinds, so to speak; the kinds are real and there to be discovered, and are independent of our subjective mental classifications. Abstracted forms are derived from individual instances; the logical rules of the combination of such forms are revealed in real definitions; the forms, through real definitions, give concepts which have fixed immutable objective meaning; the forms and their logical combination, known through their concepts, are the proper objects of knowledge. Knowledge of the forms, through real definitions, is derived from sensory experience and the intellectual faculty of abstracting general concepts from the resembling essential nature of instances of individuals of the same sort. Thus although universals do not exist as separate entities, they are objective in reflecting the extramental common defining real natures of individuals.
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