Aquinas was a medieval Christian philosopher born in 1225 CE in the city of Aquino, Italy. He is considered the most important medieval philosopher, having combined Christian theology with Greek thought, in particular the philosophy of Aristotle. Aquinas believed that God exists, is infinite, eternal, and unchanging and that this can be proven through reason. He famously offers five proofs of God’s existence, including the Argument from Design. Aquinas sees man as a composite being, body and soul, who is capable of knowing both through reason (natural revelation) and faith (supernatural revelation). Seeing happiness as the ultimate goal, Aquinas believes man is endowed with an understanding of what is right which he calls the “natural law.”
Aquinas was born during a time when latin translations of Greek philosophy, in particular Aristotle, had just been introduced to Europe. Aquinas became a Dominican monk and participated in the tradition of scholasticism, studying philosophy and other subjects at the University of Paris. He would come to believe that both reason and revelation were complimentary means of knowing things, since all truth comes from God. In this way, he would put forth would a philosophy which synthesized Aristotelian beliefs with Christian scripture, most famously in his work Summa Theologica.
Before Aquinas, Anselm had attempted to prove God’s existence through reason using what is known as the Ontological Argument. The Ontological Argument states that since one can think of something which nothing else is greater than, this thing must necessarily exist, and this is what we call God. Aquinas did not accept this argument, explaining that while such a thing would exist as a concept in our understanding, that does not mean that it exists otherwise. He would go on to offer what he believed to be more compelling arguments for the existence of God based on reason, known as the Five Proofs.
First, Aquinas puts forth what is known as the Argument of the Unmoved Mover, which explains that God must exist since there is motion in the world. Since things are in motion, something must have caused that motion. Aquinas recognizes that one can infinitely say that whatever is in motion was caused by something else (i.e. an infinite regress). Aquinas believes this is absurd, and therefore there must be some initial mover, an “Unmoved Mover,” and that is what we call God. Likewise, Aquinas puts forth a second argument, the Argument of the First Cause which says similarly that since everything has a cause, there must be a First Cause, and that is also what we call God.
Aquinas then argues that God must exist because the world exists. Since its conceivable that the world could not exist, since it does, it’s existence is contingent (“not necessary”). It’s existence must therefore be based on something that is necessary, and that thing is God. This is known as the Argument from Contingency. Aquinas also argues that since different things participate in goodness to a greater or lesser degree, there must be some standard, something that is the most good, and that would be God. This is known as the Argument from Degrees.
Lastly, Aquinas takes up Aristotle’s observation that everything in the world acts in a particular way, and he sees that as proof that nature has been designed intelligently. Aristotle explains, “Whatever lacks knowledge cannot move towards an end, unless it be directed by some being endowed with knowledge and intelligence; as the arrow is directed by the archer. Therefore, some intelligent being exists by whom all natural things are directed to their end; and this being we call God.” This is known as the Argument from Design.
For Aquinas, we can know the nature of God by realizing first what he isn’t (this is known as via negativa). Since God cannot want, cannot be limited, and cannot change, he must therefore be a simple being (i.e. without parts), which is both infinite, eternal, and free of all desires. This concept of God has been embraced by the Catholic Church. Aquinas will identify God as the source of all that is true and good.
Since all truths come from God, Aquinas maintains that we can come to understand things both through the use of reason (natural revelation) and faith (supernatural revelation). In this way, he will seek to harmonize philosophy with theology. Aquinas will famously put forward the belief that as humans we have an innate awareness of what is good, known as the “natural law.” Having been created by God, human nature contains within this natural law, which holds as its first principle that we should do good and avoid evil. Those who follow the natural law live virtuously, while those who stray live in sin.
Like Aristotle, Aquinas believes that happiness (eudaimonia) is the goal of life, and embraces Aristotle’s belief that man is a “political animal” and is best able to live well in a community with others. Society not only provides man with his basic needs, it also enables him to cultivate his virtues. In this way, Aquinas explains that not only must man follow the natural law, doing good and avoiding evil, he must also create laws to ensure that people are able to live together peacefully. For example, while as humans we desire to live and procreate, human laws are needed to make sure acts such as adultery do not go unpunished. Aquinas explains that while some people will initially only follow the law out of “force and fear,” ultimately they will do so out of a desire to live virtously.
In striving for happiness, Aquinas identifies four cardinal virtues: prudence, temperance, justice and fortitude. He explains that we should always try to do what is right and perform acts of charity, peace and holiness. However, Aquinas will also explain that true happiness can only be achieved through the grace of God. Through God’s love, those who have been chosen will be able to unite with him in what is known as the “beatific vision.” In this way, Aquinas agrees with Aristotle that happiness is the goal of life, while at the same time as a theologian will go beyond this to embrace traditional Christian beliefs such as predestination, original sin, the afterlife, and resurrection.
In addition to using Aristotle to support Christian beliefs, Aquinas also appeals to Aristotle’s understanding of the role played by the senses in acquiring knowledge. For Plato, knowledge is knowledge of the Forms. For example, to know something is beautiful is to recognize through one’s intellect that something has the Form of Beauty. In this way, Plato identifies man’s nature with his rational soul and the Intelligible world. As a consequence, the Platonic tradition sees the material world as interfering with understanding, and the soul as being trapped in the body. Because Aquinas sees the world and the body as equal parts of God’s Creation, he is critical of this position. Instead, he sees man’s nature as a composite being with both a soul and a body, and that it is through the body that knowledge is acquired. He says, “Whatever is in our intellect must have previously been in the senses.” His theory of knowledge (epistemology) will come to be known in modern times as empiricism.
Like Augustine, Aquinas will combine Christian scripture with Greek philosophy. Aquinas used his academic background (known as scholasticism) in combination with his understanding of Aristotle to create a philosophy which both supports Christian theology as well as strikes a harmony between reason and revelation. In doing so, he was influenced both by the Islamic philosopher Averroes as well as the Jewish philosopher Maimonides. His thoughts would be embraced by the Catholic Church, who considered him a saint. While his understanding of knowledge through the senses was developed in modern times as empiricism, it was also countered by those such as Descartes who see knowledge as the result of deductive reasoning (rationalism). In both philosophy as well as theology, Aquinas was the most important medieval philosopher and his thoughts shape the beliefs held by many people today.