An Introduction to the Five Ways of St. Thomas Aquinas, Part 1

Thomas Aquinas was a thirteenth century Dominican friar (1225-1274). He is regarded as the greatest medieval scholastic theologian and, along with St. Augustine of Hippo, indispensible for understanding Catholic theology and philosophy. He is best known for his two masterpieces, Summa Theologica and Summa contra Gentiles, but is also highly respected for his commentaries on the Scriptures. Along with being a great theologian and philosopher, Thomas was a mystic. Several accounts from contemporaries report having witnessed him levitating in prayer and being the recipient of heavenly visions. Thomas wrote Eucharistic hymns that are part of the Church’s liturgy, including O Salutaris Hostia and Panis Angelicus. In the spring of 1274, Thomas fell ill en route to the Second Council of Lyons, called by Pope Gregory X in hopes of reconciling Western and Eastern Christianity. He died at the Cistercian Fossanova Abbey on March 7, 1274. The breadth of subjects he considered in his writings have earned him the title, “The Common Doctor,” while his admirers have bestowed on him the title “Angelic Doctor” because of his great piety. Thomas Aquinas was canonized a saint of the Catholic Church by Pope John XXII in 1323 and declared a Doctor of the Church by Pope Pius V in 1568. His feast day is January 28.

St. Thomas Aquinas’ Five Ways for demonstrating the existence of God are included in Part I of the Summa Theologica, his great unfinished masterpiece, written as a primer for students of the Christian religion. Thomas also includes proofs for God’s existence in Chapter 13 of Summa contra Gentiles. The format of the Summa Theologica is: question, objections, answers. Thomas proposes a question, lists a series of objections, then answers those objections. For instance, Thomas asks, “Whether it is possible to demonstrate the existence of God?” He then presents three objections to the position that it is possible to demonstrate the existence of God. He then answers those objections, concluding that it is, indeed, possible to demonstrate the existence of God. This is Thomas’ pattern throughout the Summa.

Thomas’ Five Ways have often been misrepresented because they are so often misunderstood. Many of the objections to the Five Ways are based on a misreading of them, or of failing to read the Five Ways within the context of Thomas’ broader philosophy. Too often, contemporary philosophers or critics misapply modern concepts to Thomas’ thirteenth century arguments. Often enough, however, misunderstandings are based on simply not following Thomas’ argument. Though some are easier to follow than others, even for the non-philosopher, anyone who claims that Thomas’ Five Ways are easily understood or, even more telling, easily countered, likely fails to understand them. I’ve made an effort to make Thomas’ Five Ways as understandable as possible. While I hope I haven’t failed, I don’t boast prematurely.

Can it be Demonstrated that God Exists?

Before considering Thomas’ Five Ways for demonstrating the existence of God, let’s look at how Thomas concludes that it’s even possible to demonstrate the existence of God, for we’ve seen that the possibility of demonstrating God’s existence isn’t held by all. Thomas lists three objections to the notion that God’s existence can be demonstrated:

1. God’s existence can’t be demonstrated because His existence is an article of faith. Articles of faith can’t be demonstrated because faith is faith in what can’t be seen (Hebrews 11:1). We can only demonstrate the existence of things we can see, or what can otherwise be experienced by the senses. Since God can’t be seen, His existence can’t be demonstrated;

2. God’s existence can’t be demonstrated because we can’t know God’s essence. So, we can say what God is not (ie: God is not the universe, God is not a superhuman, etc…), but we can’t say what God is, because the essence of an infinite, unlimited Being simply can’t be understood by finite, limited humans;

3. God’s existence can’t be demonstrated because whether or not God exists can only be known by His effects or His impact on the world around us, somewhat like knowing the wind is there by seeing the trees and grass bending. But, God’s effects on a finite world are themselves finite, whereas God is infinite. So, His effects fail to adequately demonstrate His existence, because what is finite and limited can’t possibly be enough to demonstrate what is infinite and unlimited. Infinity is simply too vast and mystifying to be explained by the finite.

In the next article, I’ll present how Thomas answers these objections.

Be Christ for all. Bring Christ to all. See Christ in all.