The Five Ways explained (ST I, q. 2, a. 3)
Summa article explained, no. 1. A paraphrase and reading guide, not a translation.
Why start here
Most people meet the Five Ways as a list of five proofs lifted out of the Summa. Read in place, the article is shorter and more modest than its reputation. It is a disputed question with a fixed shape, and the shape is the lesson. If you learn to read this one, you can read the other articles of the Summa the same way.
The shape of every article
- The question, put as "whether": Whether God exists?
- Objections: the strongest case for the answer Aquinas will reject. They are stated fairly, and they are often good.
- Sed contra ("on the contrary"): an authority pointing the other way. It is not the argument. It shows the question is open.
- Respondeo ("I answer that"): Aquinas's own reasoning.
- Replies to the objections: each objection answered in turn, often by drawing a distinction.
Skip the objections and you misread the article. Aquinas wrote the answer to meet them.
The objections
First objection, from evil. If one of two contraries were infinite, the other would be wholly destroyed. By "God" we mean an infinite good. So if God existed, no evil would be found. But there is evil in the world. Therefore God does not exist.
Second objection, from economy. What can be accounted for by fewer principles should not be accounted for by more. Natural things are explained by nature; deliberate things by human reason and will. Nothing seems to require God.
Notice what these are: the problem of evil and an early form of "we don't need that hypothesis". Aquinas opens the most famous article on God's existence with the two objections that still carry most weight.
Sed contra
God says of himself, in Exodus 3:14, "I am who am". That is all. The authority does not prove anything; it marks the question as one the tradition has an answer to.
Respondeo: the five ways
Aquinas says God's existence can be shown in five ways. Each starts from something observed in the world.
- From motion (change). Things change. Whatever changes is changed by another. An infinite series of changers that are themselves changed would explain nothing, so there must be a first changer not itself changed.
- From efficient causes. There is an order of causes. Nothing causes itself, and an infinite series of dependent causes gives no first cause and so no intermediate or last one. There must be a first efficient cause.
- From possibility and necessity. Some things can be and not be. If everything were like that, at some time nothing would have been, and then nothing could begin. So something must exist necessarily, and ultimately something necessary of itself.
- From gradation. We find more and less good, true and noble in things. "More" and "less" are said by reference to a maximum. There is something that is the cause of being, goodness and every perfection in things.
- From the governance of things. Things without knowledge act for an end, as shown by their acting always or nearly always in the same way to the best result. What lacks knowledge does not tend to an end unless directed by something with knowledge, as the arrow by the archer.
Each way ends with a version of the same short sentence: and this everyone understands to be God. That phrase claims less than people think. The proof of what that first cause is like (simple, perfect, good, one) comes in the questions that follow, q. 3 to q. 11.
The replies
To the first (evil). Aquinas answers with Augustine (Enchiridion xi): since God is the highest good, he would not allow any evil in his works unless he were so powerful and good as to bring good even out of evil. Evil is permitted, not overlooked.
To the second (economy). Nature works for a determinate end under the direction of a higher agent, so what nature does must also be traced back to God as first cause. And what is done by design must be traced to something higher than human reason and will, which can change and fail.
Common misreadings
- "These are five independent proofs." They share a structure: an observed feature of the world, a dependence, and the impossibility of an explanation that never arrives at a first term.
- "The infinite regress step means time had to begin." In the first two ways the series is of causes acting now, not of events in the past. Aquinas himself held that the world's beginning is held by faith alone and cannot be demonstrated (I, q. 46, a. 2). In the same article (reply to objection 7) he distinguishes an infinite series of causes that depend on each other here and now, which is impossible, from an accidental series stretching back in time, which reason cannot rule out.
- "The article proves the Christian God." It concludes to a first cause. Aquinas builds the rest slowly, and he holds that the Trinity cannot be known by natural reason (I, q. 32, a. 1).
How to work this article in Aquinian Studio
Aquinian is a reasoning study after the method of Aquinas. Put the question to it in disputation form and it distinguishes the terms first, orders the authorities, and states the strongest objection before answering. A second pass is allowed to wound the first. It reasons with authority; it does not become authority, and it is not a priest or a substitute for your tutor or confessor.
Try it on the first objection: ask whether Augustine's reply actually meets the force of the argument, and see which distinction it draws. aquinian.com. New accounts start with 150 free credits, no card.
FAQ
What are Aquinas's Five Ways? Five arguments in Summa Theologiae I, q. 2, a. 3 for God's existence, from change, efficient causes, possibility and necessity, gradation, and the governance of things.
Where are the Five Ways in the Summa? First Part, question 2, article 3.
Does Aquinas answer the problem of evil in the Five Ways article? Yes, in the reply to the first objection, drawing on Augustine: God would not permit evil unless he could bring good out of it.
Do the Five Ways assume the universe began in time? No. Aquinas held that reason alone cannot prove the world began (I, q. 46, a. 2). The first two ways concern causes acting now.