Saint Thomas (1225–74), Italian philosopher-theologian, the most influential thinker of the medieval period. He produced a powerful philosophical synthesis that combined Aristotelian and Neoplatonic elements within a Christian context in an original and ingenious way. Life and works. Thomas was born at Aquino castle in Roccasecca, Italy, and took early schooling at the Benedictine Abbey of Monte Cassino. He then studied liberal arts and philosophy at the University of Naples (1239–44) and joined the Dominican order. While going to Paris for further studies as a Dominican, he was detained by his family for about a year. Upon being released, he studied with the Dominicans at Paris, perhaps privately, until 1248, when he journeyed to Cologne to work under Albertus Magnus. Thomas’s own report (reportatio) of Albertus’s lectures on the Divine Names of Dionysius and his notes on Albertus’s lectures on Aristotle’s Ethics date from this period. In 1252 Thomas returned to Paris to lecture there as a bachelor in theology. His resulting commentary on the Sentences of Peter Lombard dates from this period, as do two philosophical treatises, On Being and Essence (De ente et essentia) and On the Principles of Nature (De principiis naturae).
In 1256 he began lecturing as master of theology at Paris. From this period (1256–59) date a series of scriptural commentaries, the disputations On Truth (De veritate), Quodlibetal Questions VII –XI, and earlier parts of the Summa against the Gentiles (Summa contra gentiles; hereafter SCG). At different locations in Italy from 1259 to 1269, Thomas continued to write prodigiously, including, among other works, the completion of the SCG; a commentary on the Divine Names; disputations On the Power of God (De potentia Dei) and On Evil (De malo); and Summa of Theology (Summa theologiae; hereafter ST), Part I. In January 1269, he resumed teaching in Paris as regent master and wrote extensively until returning to Italy in 1272. From this second Parisian regency date the disputations On the Soul (De anima) and On Virtues (De virtutibus); continuation of ST; Quodlibets I–VI and XII; On the Unity of the Intellect against the Averroists (De unitate intellectus contra Averroistas); most if not all of his commentaries on Aristotle; a commentary on the Book of Causes (Liber de causis); and On the Eternity of the World (De aeternitate mundi). In 1272 Thomas returned to Italy where he lectured on theology at Naples and continued to write until December 6, 1273, when his scholarly work ceased. He died three months later en route to the Second Council of Lyons. Doctrine. Aquinas was both a philosopher and a theologian. The greater part of his writings are theological, but there are many strictly philosophical works within his corpus, such as On Being and Essence, On the Principles of Nature, On the Eternity of the World, and the commentaries on Aristotle and on the Book of Causes. Also important are large sections of strictly philosophical writing incorporated into theological works such as the SCG, ST, and various disputations. Aquinas clearly distinguishes between strictly philosophical investigation and theological investigation. If philosophy is based on the light of natural reason, theology (sacra doctrina) presupposes faith in divine revelation. While the natural light of reason is insufficient to discover things that can be made known to human beings only through revelation, e.g., belief in the Trinity, Thomas holds that it is impossible for those things revealed to us by God through faith to be opposed to those we can discover by using human reason. For then one or the other would have to be false; and since both come to us from God, God himself would be the author of falsity, something Thomas rejects as abhorrent. Hence it is appropriate for the theologian to use philosophical reasoning in theologizing. Aquinas also distinguishes between the orders to be followed by the theologian and by the philosopher. In theology one reasons from belief in God and his revelation to the implications of this for created reality. In philosophy one begins with an investigation of created reality insofar as this can be understood by human reason and then seeks to arrive at some knowledge of divine reality viewed as the cause of created reality and the end or goal of one’s philosophical inquiry (SCG II, c. 4). This means that the order Aquinas follows in his theological Summae (SCG and ST) is not the same as that which he prescribes for the philosopher (cf. Prooemium to Commentary on the Metaphysics). Also underlying much of Aquinas’s thought is his acceptance of the difference between theoretical or speculative philosophy (including natural philosophy, mathematics, and metaphysics) and practical philosophy. Being and analogy. For Aquinas the highest part of philosophy is metaphysics, the science of being as being. The subject of this science is not God, but being, viewed without restriction to any given kind of being, or simply as being (Prooemium to Commentary on Metaphysics; In de trinitate, qu. 5, a. 4). The metaphysician does not enjoy a direct vision of God in this life, but can reason to knowledge of him by moving from created effects to awareness of him as their uncreated cause. God is therefore not the subject of metaphysics, nor is he included in its subject. God can be studied by the metaphysician only indirectly, as the cause of the finite beings that fall under being as being, the subject of the science. In order to account for the human intellect’s discovery of being as being, in contrast with being as mobile (studied by natural philosophy) or being as quantified (studied by mathematics), Thomas appeals to a special kind of intellectual operation, a negative judgment, technically named by him ‘separation.’ Through this operation one discovers that being, in order to be realized as such, need not be material and changing. Only as a result of this judgment is one justified in studying being as being.
Following Aristotle (and Averroes), Thomas is convinced that the term ‘being’ is used in various ways and with different meanings. Yet these different usages are not unrelated and do enjoy an underlying unity sufficient for being as being to be the subject of a single science. On the level of finite being Thomas adopts and adapts Aristotle’s theory of unity by reference to a first order of being. For Thomas as for Aristotle this unity is guaranteed by the primary referent in our predication of being – substance. Other things are named being only because they are in some way ordered to and dependent on substance, the primary instance of being. Hence being is analogous. Since Thomas’s application of analogy to the divine names presupposes the existence of God, we shall first examine his discussion of that issue.
The existence of God and the ‘five ways.’ Thomas holds that unaided human reason, i.e., philosophical reason, can demonstrate that God exists, that he is one, etc., by reasoning from effect to cause (De trinitate, qu. 2, a. 3; SCG I, c. 4). Best-known among his many presentations of argumentation for God’s existence are the ‘five ways.’ Perhaps even more interesting for today’s student of his metaphysics is a brief argument developed in one of his first writings, On Being and Essence (c.4). There he wishes to determine how essence is realized in what he terms ‘separate substances,’ i.e., the soul, intelligences (angels of the Christian tradition), and the first cause (God).
After criticizing the view that created separate substances are composed of matter and form, Aquinas counters that they are not entirely free from composition. They are composed of a form (or essence) and an act of existing (esse). He immediately develops a complex argument: (1) We can think of an essence or quiddity without knowing whether or not it actually exists. Therefore in such entities essence and act of existing differ unless (2) there is a thing whose quiddity and act of existing are identical. At best there can be only one such being, he continues, by eliminating multiplication of such an entity either through the addition of some difference or through the reception of its form in different instances of matter. Hence, any such being can only be separate and unreceived esse, whereas esse in all else is received in something else, i.e., essence. (3) Since esse in all other entities is therefore distinct from essence or quiddity, existence is communicated to such beings by something else, i.e., they are caused. Since that which exists through something else must be traced back to that which exists of itself, there must be some thing that causes the existence of everything else and that is identical with its act of existing. Otherwise one would regress to infinity in caused causes of existence, which Thomas here dismisses as unacceptable. In qu. 2, a. 1 of ST I Thomas rejects the claim that God’s existence is self-evident to us in this life, and in a. 2 maintains that God’s existence can be demonstrated by reasoning from knowledge of an existing effect to knowledge of God as the cause required for that effect to exist. The first way or argument (art. 3) rests upon the fact that various things in our world of sense experience are moved. But whatever is moved is moved by something else. To justify this, Thomas reasons that to be moved is to be reduced from potentiality to actuality, and that nothing can reduce itself from potency to act; for it would then have to be in potency (if it is to be moved) and in act at the same time and in the same respect. (This does not mean that a