Thomism is the philosophical school that followed in the legacy of St. Thomas Aquinas and lead to the canonization of the original dogma of the Roman Catholic Church. The word comes from the name of its originator, whose summary work Summa Theologica has arguably been second to only the Bible in importance to the Catholic Church.
Saint Thomas was important in shifting the influence of medieval philosophy (also known as Scholasticism) away from Plato and towards Aristotle. In this he was influenced by contemporary Arabic philosophy, especially the work of Averroes. The ensuing school of thought, through its influence on Catholicism and the ethics of the Catholic school, is by any standard one of the most influential philosophies of all time, also significant due to the sheer number of people living by its teachings. Thomism also influenced the birth of Protestantism, which arose partially as a reaction to the authoritarian, Thomic dogma of the Catholic Church.
Thomism prevailed and became the official dogma of the Catholic Church, offering a coherent, logical, and clear metaphysical picture of both the material and spiritual worlds. It prevailed as a coherent system until the discovery of Newtonian mechanics, which contradicted the Aristotelian physics, thereby discrediting supplanting much of the thomistic ontology. However, the ethical parts of Thomism, as well as a large part of its views on life, humans, and theology, transcended into the various schools of Neothomism that are the official dogma of the Roman Catholic Church today.
Aquinas worked to create a philosophical system which integrated Christian doctrine with elements taken from the philosophy of Aristotle. Generally, he augmented the Neo-Platonic view of philosophy which, after Augustine, had become tremendously influential amongst medieval philosophers, with insights drawn from Aristotle. In this he was greatly influenced by his reading of contemporary Arabic philosophers, especially Averroes. Aquinas, is, therefore, generally agreed to have moved the focus of Scholastic philosophy from Plato to Aristotle. The extent to which he was successful in doing this is, of course, still hotly debated.
(Commentary from the Schaff-Herzog Encyclopedia of Religion:)
Aquinas's two most important qualities were his great talent for systematizing and his power of simple and lucid exposition. The work of preceding generations, especially of Alexander of Hales, had lightened the task of selection and ordering of the material; on the other hand, it had added to the number of problems and expanded the argument enormously, impairing the unity and clarity of the progress of thought. It was Thomas who made a single connected and consistent whole of the mass. His Aristotelianism, with its Neoplatonic elements, should also be noted. He owed not only his philosophical thoughts and world conception to Aristotle, but also the frame for his theological system; Aristotle's metaphysics and ethics dictated the trend of his system. Here he gained the purely rational framework for his massive temple of thought, namely of God, the rational cause of the world, and man's striving after him. Then he filled this in with the dogmas of the Church or of revelation. Nevertheless he succeeded in upholding church doctrine as credible and reasonable. The final characteristic of Thomas to be noted is his blameless orthodoxy. For opposition to Thomas and the reaction in the fifteenth century, see Scholasticism. This position as the teacher of the church grew stronger from Pope Leo X (1520) to Leo XIII (1900); even to-day the Roman Catholic Church preserves the inheritance of the ancient world-conception and the old church dogmas in the form which Thomas Aquinas gave them. For the relation of theology to philosophy and the sphere of the former and its sources, see Scholasticism.
See articles Summa Theologica and Summa Contra Gentiles for more detailed discussion of Aquinas's philosophy.
His Five Ways to prove the existence of God
Aquinas shows five ways (he calls them ways instead of proofs) to indicate the existence of God, some of which are developed in detail (especially the first) in his Summa Contra Gentiles.
The first way
(Prime Mover) "It is clear that there are in this world things which are moved. Now, every object which is moved receives that movement from another. If the motor is itself moved, there must be another motor moving it, and after that yet another, and so on. But it is impossible to go on indefinitely, for then there would be no first motor at all, and consequently no movement" ("Contra Gentiles," ii. 33). This proof might be taken from Maimonides, whose seventeenth proposition reads: "All that which is moved has necessarily a motor" (Guide of the Perplexed, II:16). Since he was more or less a contemporary (being of the previous century), it could also be parallel discovery or a source shared by both, for example one of several Arab sources.
The second way
"We discern in all sensible things a certain chain of efficient causes. We find, however, nothing which is its own efficient cause, for that cause would then be anterior to itself. On the other side, it is impossible to ascend from cause to cause indefinitely in the series of efficient causes....There must therefore exist one self-sufficient, efficient cause, and that is God" ("Contra Gent." i. 22). This is similar to the argument in Bahya ibn Pakuda's Duties of the Heart (chapter on "Unity," 5) and Maimonides' argument in the Guide, II:16.
The third way
"We find in nature things which may be and may not be, since there are some who are born and others who die; they consequently can exist or not exist. But it is impossible that such things should live for ever, for there is nothing which may be as well as not be at one time. Thus if all beings need not have existed, there must have been a time in which nothing existed. But, in that case, nothing would exist now; for that which does not exist can not receive life but from one who exists; . . . there must therefore be in nature a necessarily existent being." This proof might be based on Avicenna's doctrine of a necessary and possible being, and is expounded by Maimonides in the Guide, II:19.
The fourth way
Any category has its degrees, such as good and better, warm and warmer. Each also has one thing that's the ultimate of that measure, like good and "best", warm and "hottest". And whatever is the most of that category is the source of that category, as fire (or, in modern terms, energy itself) is the source of heat, and God must therefore be the source of goodness.
The fifth way
(Intelligent Design) Everything, sentient or otherwise, progresses in an orderly way. Planets move in their orbits, light breaks from and combines into its spectrum, et cetera. Reality has a natural order, which could not have come from nothing, yet which preceeds mere humans. This could only be explained by some higher power...the Creator...having set things so.
Demonstrating God's creative power
In order to demonstrate God's creative power, Thomas says: "If a being participates, to a certain degree, in an 'accident,' this accidental property must have been communicated to it by a cause which possesses it essentially. Thus iron becomes incandescent by the action of fire. Now, God is His own power which subsists by itself. The being which subsists by itself is necessarily one" ("Summa Theol." i. 44, art. 1). This idea is also expounded by Bahya ibn Pakuda in his "Duties of the Heart."
Connection with Jewish thought
Jewish philosophical influences on Aquinas
Aquinas did not disdain to draw upon Jewish philosophical sources. His main work, "Summa Theologię," shows a profound knowledge not only of the writings of Avicebron (Ibn Gabirol), whose name he mentions, but of most Jewish philosophical works then existing.
Thomas pronounces himself energetically against the hypothesis of the eternity of the world. But as this theory is attributed to Aristotle, he seeks to demonstrate that the latter did not express himself categorically on this subject. "The argument," said he, "which Aristotle presents to support this thesis is not properly called a demonstration, but is only a reply to the theories of those ancients who supposed that this world had a beginning and who gave only impossible proofs. There are three reasons for believing that Aristotle himself attached only a relative value to this reasoning. . . ." ("Summa Theologię," i. 45, art. 1). In this Thomas copies word for word Maimonides's Guide for the Perplexed, where those reasons are given (I:2,15).
Aquinas' influence on Jewish thought
Aquinas' doctrines, because of their close relationship with those of Jewish philosophy, found great favor among Jews. Judah Romano (born 1286) translated Aquinas' ideas from Latin into Hebrew under the title "Ma'amar ha-Mamschalim," together with other small treatises extracted from the "Contra Gentiles" ("Neged ha-Umot").
Eli Hobillo (1470) translated, without Hebrew title, the "Quęstiones Disputatę," "Quęstio de Anima," his "De Animę Facultatibus," under the title "Ma'amar be-KoḦot ha-Nefesh," (edited by Jellinek); his "De Universalibus" as "Be-Inyan ha-Kolel"; "Shaalot Ma'amar beNimẓa we-biMehut."
Abraham Nehemiah ben Joseph (1490) translated Thomas' "Commentarii in Metaphysicam." According to Moses Almosnino, Isaac Abravanel desired to translate the "Quęstio de Spiritualibus Creaturis." Abravanel indeed seems to have been well acquainted with the philosophy of Thomas Aquinas, whom he mentions in his work "Mif'alot Elohim" (vi. 3). The physician Jacob Zahalen (d. 1693) translated some extracts from the "Summa Theologię Contra Gentiles."
Thomism and modern philosophy
In describing Thomism as a philosophy of common sense, G.K. Chesterton wrote:
- "Since the modern world began in the sixteenth century, nobody's system of philosophy has really corresponded to everybody's sense of reality; to what, if left to themselves, common men would call common sense. Each started with a paradox; a peculiar point of view demanding the sacrifice of what they would call a sane point of view. That is the one thing common to Hobbes and Hegel, to Kant and Bergson, to Berkeley and William James. A man had to believe something that no normal man would believe, if it were suddenly propounded to his simplicity; as that law is about right, or right is outside reason, or things are only as we think them, or everything is relative to a reality that is not there. The modern philosopher claims, like a sort of confidence man, that if once we will grant him this, the rest will be easy; he will straighten out the world, if once he is allowed to give this one twist to the mind...
- Against all this the philosophy of St. Thomas stands founded on the universal common conviction that eggs are eggs. The Hegelian may say that an egg is really a hen, because it is a part of an endless rocess of Becoming; the Berkelian may hold that poached eggs only exist as a dream exists, since it is quite as easy to call the dream the cause of the eggs as the eggs the cause of the dream; the Pragmatist may believe that we get the best out of scrambled eggs by forgetting that they ever were eggs, and only remembering the scramble. But no pupil of St. Thomas needs to addle his brains in order adequately to addle his eggs; to put his head at any peculiar angle in looking at eggs, or squinting at eggs, or winking the other eye in order to see a new simplication of eggs. The Thomist stands in the broad daylight of the brotherhood of men, in their common consciousness that eggs are not hens or dreams or mere practical assumptions; but things attested by the Authority of the Senses, which is from God." (Chesterton, St. Thomas Aquinus, p. 136).