Philosophy of St Thomas Aquinas

Roman Catholic Theologian Known for Summa Contra Gentiles

Apr 22, 2009

Thomas Aquinas' the "Five Ways" philosophical arguments from Summa Theologica, his most important work.

Thomas Aquinas (125-1274), was born in northern Sicily,. He was first educated at the University of Naples and later at Cologne. He was canonized by Pope XII in 1323.

St. Thomas Aquinas, Theologian and Philosopher

Aquinas lectured at Paris and Naples. He joined the Dominican order, followed Albertus Magnus to Paris in 1245.

Since then, he refused ecclesiastical dignities in order to preach and work on Summa Theologica. He argued that "revelation" could not conflict with reason, and while separate, rested on one absolute truth.

While much of Aquinas' work was derived from Aristotelian thoughts, he also extended many of Aristotle's ideas and made original contributions. Among his significant achievements are the "Five Ways" or five proofs of God's existence, from Summa Theologica, which Aquinas logically argues in a most clear and succinct manner.

Aquinas claims that the existence of God can be proved by considering the concept of change. In the process, change must be caused by change, also caused by something other than itself, and so on, ad infinitum.

Clearly, there must be something which is the cause of all change, but which itself does not undergo change. The first mover, Aquinas concludes, is God.

Aquinas' Second Way Proof

Aquinas notes that causes always operate in series, however, there must be a first cause of the series, or else, there can't be a series at all.

Like the First Way, the Second Way proceeds on the assumption that a thing cannot cause itself. His conclusion, therefore, is that there is a thing which does cause itself, which is God.

Critics and other philosophers have criticized this form of arguing as confused, since the proposition that appears to be proven in the conclusion is the very same proposition denied in the argument.

Aquinas' Third Way Proof

Aquinas notes that worldly things come to be and pass away but then not everything can be like this, for then there would have been time when nothing existed. But if that were true then nothing could have ever come to being, since something cannot come from nothing. Therefore something must have always existed, and this is God.

Aquinas' Fourth Way Proof

Aquinas offers a version of the Ontological Argument. He notes that some things exhibit varying degrees of in terms of quality. For example, a thing may be more-or-less hot or more-or-less cold. Such varying degrees of quality are caused by something that contains the most or perfect amount of that quality. That which is most good is, which of course, is God.

Aquinas' Fifth Way Proof

In this last Way, Aquinas relies on Aristotle's notion of "telos" or purpose, that is, all things aim towards some ultimate goal or end. However, to be guided by a purpose or a goal implies a mind that directs that purpose.

According to Aquinas that director once again is God. Versions of Aquinas's cosmological and ontological arguments are still accepted by the Catholic Church, although some modern philosophers have almost rejected all five of Aquinas's Ways.

The first, second and third Ways of Aquinas's arguments are variations of a more general argument, the Cosmological Argument. Summa synthesized all human knowledge by reconciling Aristotle and Christianity.

Books by St Thomas Aquinas

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