Thomism is the philosophical and theological school which arose as a legacy of the work and thought of Thomas Aquinas (1225–1274), a Dominican philosopher, theologian, and Doctor of the Church.
In philosophy, Thomas's disputed questions and commentaries on Aristotle are perhaps his best-known works. In theology, his Summa Theologica is amongst the most influential documents in medieval theology and continues to be the central point of reference for the philosophy and theology of the Catholic Church. In the 1914 motu proprio Doctoris Angelici, Pope Pius X cautioned that the teachings of the Church cannot be understood without the basic philosophical underpinnings of Thomas's major theses: Accessed 25 October 2012
Overview
Thomas Aquinas held and practiced the principle that truth is to be accepted no matter where it is found. His doctrines drew from Greek, Roman, Islamic and Jewish philosophers. Specifically, he was a realist (i.e. unlike skeptics, he believed that the world can be known as it is).Summa, I, Q.85, art.2. "Some have asserted that our intellectual faculties know only the impression made on them; as, for example, that sense is cognizant only of the impression made on its own organ. According to this theory, the intellect understands only its own impression, namely, the intelligible species which it has received, so that this species is what is understood. This is, however, manifestly false for two reasons [...]" He often affirmed Aristotle's views with independent arguments, and largely followed Aristotelian terminology and metaphysics. He wrote comprehensive commentaries on Aristotle, and respectfully referred to him simply as "the Philosopher".E.g., Summa Theologiæ, Q.84, art.7. , where the sed contra is only a quote from Aristotle's De anima.
He also adhered to some neoplatonic principles, for example that "it is absolutely true that there is first something which is essentially being and essentially good, which we call God, [...] [and that] everything can be called good and a being, inasmuch as it participates in it by way of a certain assimilation".
Metaphysics Aquinas says that the fundamental axioms of ontology are the principle of non-contradiction and the principle of causality. Therefore, any being that does not contradict these two laws could theoretically exist,De Ente et Essentia, 67–68. "Although everyone admits the simplicity of the First Cause, some try to introduce a composition of matter and form in the intelligences and in souls... But this is not in agreement with what philosophers commonly say, because they call them substances separated from matter, and prove them to be without all matter." even if said being were incorporeal.
Predication
Aquinas noted three forms of descriptive language when predicating: univocal, analogical, and equivocal. Univocality is the use of a descriptor in the same sense when applied to two objects or groups of objects. For instance, when the word "milk" is applied both to milk produced by cows and by any other female mammal. Analogy occurs when a descriptor changes some but not all of its meaning. For example, the word "healthy" is analogical in that it applies both to a person or animal which enjoys good health and to some food or drink which promotes health. Equivocation is the complete change in meaning of the descriptor and is an informal fallacy, for example when the word "bank" is applied to river banks and financial banks. Modern philosophers call it ambiguity.
Further, the usage of "definition" that Aquinas gives is the genus of the being, plus a difference that sets it apart from the genus itself. For instance, the Aristotelian definition of "man" is "rational animal"; its genus being animal, and what sets apart man from other animals is his rationality.
Being
In Thomist philosophy, the definition of a being is "that which is", a principle with two parts: "that which" refers to its quiddity (literally "whatness"), and "is" refers to its esse (Latin "to be").De Ente et Essentia, 83. "And this is why substances of this sort are said by some to be composed of "that by which it is" and "that which is", or as Boethius says, of "that which is" and "existence."" Quiddity means an essence, form, or nature which may or may not exist; whereas esse refers to existence or reality. That is, a being is "an essence that exists."Summa, I, Q.3, art.4. "Therefore, if the existence of a thing differs from its essence, this existence must be caused either by some exterior agent or by its essential principles."
Being is divided in two ways: that which is in itself (substances), and that which is in another (accidents). Substances are things which exist per se or in their own right. Accidents are qualities that apply to other things, such as shape or color: "[A]ccidents must include in their definition a subject which is outside their genus." Because they only exist in other things, Aquinas holds that metaphysics is primarily the study of substances, as they are the primary mode of being. "And because accidents are not composed of matter and form, their genus cannot be taken from matter and their difference from form, as in the case of composed substances."
The Catholic Encyclopedia pinpoints Aquinas' definition of quiddity as "that which is expressed by its definition." The quiddity or form of a thing is what makes the object what it is: "[T]hrough the form, which is the actuality of matter, matter becomes something actual and something individual", and also, "the form causes matter to be."Summa, I, Q.75, art.5. The meaning of this sentence can be altered depending on how the Latin word used in this sentence, "materiæ", is translated into English. An alternate rendering of this sentence is "The form causes matter to be what it is. Thus, it consists of two parts: "prime matter" (matter without form), and substantial form, which is what causes a substance to have its characteristics. For instance, an animal can be said to be a being whose matter is its body, and whose soulThe Aristotelian and Thomist definition of the "soul" does not refer to spirit, but is perhaps better translated as "life force." Hence, plants have souls in the sense that they are living beings. The human soul is unique in that it has consciousness. Cf. De anima, Bk. I. is its substantial form.De Principiis Naturæ, 5. "But, just as everything which is in potency can be called matter, so also everything from which something has existence whether that existence be substantial or accidental, can be called form; for example man, since he is white in potency, becomes actually white through whiteness, and sperm, since it is man in potency, becomes actually man through the soul." Together, these constitute its quiddity/essence.
All real things have the transcendental properties of being: oneness, truth, goodness (that is, all things have a final cause and therefore a purpose), etc.
Causality Aristotle categorized causality into four subsets in the Metaphysics, which is an integral part of Thomism:
(a) refers to the material cause, what a being's matter consists of (if applicable). (b) refers to the formal cause, what a being's essence is. (c) refers to the efficient cause, what brings about the beginning of, or change to, a being. (d) refers to the final cause, what a being's purpose is.
Unlike many ancient Greeks, who thought that an infinite regress of causality is possible (and thus held that the universe is uncaused), Aquinas argues that an infinite chain never accomplishes its objective and is thus impossible. Hence, a first cause is necessary for the existence of anything to be possible. Further, the First Cause must continuously be in action (similar to how there must always be a first chain in a chain link), otherwise the series collapses:
Thus, both Aristotle and Aquinas conclude that there must be an uncaused Primary Mover,Summa, I, Q.2, art.3. "The third way is taken from possibility and necessity, and runs thus..." because an infinite regress is impossible.
However, the First Cause does not necessarily have to be temporally the first. Thus, the question of whether or not the universe can be imagined as eternal was fiercely debated in the Middle Ages. The University of Paris's condemnation of 1270 denounced the belief that the world is eternal. Aquinas' intellectual rival, Bonaventure, held that the temporality of the universe is demonstrable by reason.Davis, Richard. "Bonaventure and the Arguments for the Impossibility of an Infinite Temporal Regression", American Catholic Philosophical Quarterly 70, no. 3 (Summer 1996): pp. 361–380. Poiesis: Philosophy Online, EBSCOhost (Retrieved 13 April 2010): 380. Aquinas' position was that the temporality of the world is an article of faith, and not demonstrable by reason; one could reasonably conclude either that the universe is temporal or that it is eternal.
Goodness As per the Nicomachean Ethics of Aristotle, Aquinas defines "the good" as what all things strive for. E.g., a cutting knife is said to be good if it is effective at its function, cutting. As all things have a function/final cause, all real things are good. Consequently, evil is nothing but privatio boni, or "lack of good", as Augustine of Hippo defined it.Augustine of Hippo. Enchridion, chp. 11.
Commentating on the aforementioned, Aquinas says that "there is no problem from the fact that some men desire evil. For they desire evil only under the aspect of good, that is, insofar as they think it good. Hence their intention primarily aims at the good and only incidentally touches on the evil."
As God is the ultimate end of all things, God is by essence goodness itself. Furthermore, since love is "to wish the good of another", true love in Thomism is to lead another to God. Hence why John the Evangelist says, "Whoever is without love does not know God, for God is love."
Existence of God
Thomas Aquinas holds that the existence of God can be demonstrated by reason, a view that is taught by the Catholic Church.Catechism of the Catholic Church, CCC 34. The quinque viae (Latin: five ways) found in the Summa Theologica (I, Q.2, art.3) are five possible ways of demonstrating the existence of God,Aquinas offers more metaphysical explanations for the existence of God in De Ente et Essentia and elsewhere, though the Quinquae viae are the most well-known and most commonly analyzed among these. which today are categorized as: 1. Argumentum ex motu, or the argument of the unmoved mover; 2. Argumentum ex ratione causae efficientis, or the argument of the first cause; 3. Argumentum ex contingentia, or the argument from contingency; 4. Argumentum ex gradu, or the argument from degree; and 5. Argumentum ex fine, or the teleological argument. Despite this, Aquinas also thought that sacred mysteries such as the Trinity could only be obtained through revelation; though these truths cannot contradict reason:
Aquinas responds to the problem of evil by saying that God allows evil to exist so that good may come of itSumma Contra Gentiles, Bk. III, Q.10. "Thus, it is... that evil is only caused by good accidentally." (for goodness done out of free will is superior than goodness done from biological imperative), but does not personally cause evil Himself.
View of God