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Thomism

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Thomism is a major philosophical and theological school of thought. It is based on the work of Thomas Aquinas. He was a Dominican philosopher and theologian who lived from 1225 to 1274. Aquinas is known as a Doctor of the Church. His writings remain the central point of reference for the Catholic Church.

Santo Tomás de Aquino - Juan de Peñalosa (cropped)
Santo Tomás de Aquino - Juan de Peñalosa (cropped)

His most influential work is the Summa Theologica. This document shaped medieval theology. In 1914, Pope Pius X noted that Church teachings rely on Aquinas's philosophical foundations.

SummaTheologiae
SummaTheologiae

Aquinas practiced a principle of radical intellectual openness. He believed truth should be accepted wherever it is found. Because of this, his doctrines drew from Greek, Roman, Islamic, and Jewish thinkers. He was a realist. This means he believed the world can be known exactly as it is. He relied heavily on the works of Aristotle.

Thomas Aquinas in Stained Glass crop
Thomas Aquinas in Stained Glass crop

Aquinas often referred to Aristotle simply as "the Philosopher." He used Aristotelian terminology and metaphysics to build his own arguments. He also incorporated some Neoplatonic principles regarding the nature of God.

In Thomist metaphysics, the study of being is central. Aquinas defined a being as "that which is." This concept has two parts: quiddity and esse. Quiddity is the essence or the "whatness" of a thing. Esse refers to its actual existence or reality.

Benozzo Gozzoli - Triumph of St Thomas Aquinas - WGA10334
Benozzo Gozzoli - Triumph of St Thomas Aquinas - WGA10334

A being is essentially an essence that exists. Aquinas divided being into two categories: substances and accidents. Substances are things that exist in their own right. Accidents are qualities, such as color or shape, that only exist within a substance. Therefore, metaphysics focuses primarily on studying substances.

Aquinas also explained how substances are constructed. He used the concept of matter and form. He described "prime matter" as matter without any form. Substantial form is what causes matter to become a specific, individual thing. For example, in an animal, the body is the matter and the soul is the substantial form. In this context, the "soul" is defined as a life force rather than a spirit. This form gives matter its characteristics. This process creates the quiddity or essence of the being.

To understand how things change, Aquinas used four types of causality. The first is the material cause, which is what a being is made of. The second is the formal cause, which is the being's essence. The third is the efficient cause, which starts a change or a beginning. The fourth is the final cause, which is the purpose of the being.

Thomas Aquinas in Stained Glass crop
Thomas Aquinas in Stained Glass crop

Aquinas argued that an infinite chain of causes is impossible. An infinite regress cannot accomplish an objective. Therefore, there must be a First Cause or an uncaused Primary Mover. This First Cause must remain in continuous action to prevent the chain from collapsing.

Aquinas also addressed the nature of goodness and evil. He defined "the good" as that which all things strive for. He believed all real things have a purpose, or a final cause, and are therefore good. He followed the idea that evil is not a thing itself. Instead, he called evil "privatio boni," which means a lack of good. He argued that people desire evil only because they mistakenly perceive some good within it. In this view, God is the ultimate source of goodness. True love is defined as wishing the good of another to lead them toward God.

One of the most famous parts of Thomism is the demonstration of God's existence. Aquinas proposed five logical paths known as the quinque viae. These are the five ways to prove God through reason. The first is the argument of the unmoved mover. The second is the argument of the first cause. The third is the argument from contingency. The fourth is the argument from degree. The fifth is the teleological argument, which looks at purpose.

SummaTheologiae
SummaTheologiae

While reason can prove God's existence, Aquinas believed certain mysteries, like the Trinity, require divine revelation.

Finally, Thomism provides a specific view of God's nature. Aquinas argued that God is the only being whose existence is identical to His essence. In humans, what we are is different from the fact that we exist. In God, "what He is" and "that He is" are the same. This means God cannot be made of matter or parts. He is described as simple, infinite, and omnipotent. He is also described as being goodness itself. This framework connects logical reasoning with religious faith.

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