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Chloe's essay

Essay topic:

What is the argument of Aquinas' fifth way? Is this argument valid? Is it sound? Is it persuasive?

St. Thomas Aquinas was born in 1225 in the ancient kingdom of Sicily. After being ordained as a priest in 1250, he began teaching and writing at the University of Paris in 1252. Aquinas was to become one of the leading philosophers of his day, writing extensively on theological issues, and laying down many of the principles of modern philosophy.

Aquinas' aim in The Five Ways was to provide proof for the existence of God 1. The text takes the form of a cosmological argument, made up of five points: the nature of motion; the efficiency of causes; the existence of non-contingent beings; the gradation of beings; the evidence of design. For Aquinas each of these points taken individually and in combination leads to one conclusion - that God exists. In this essay I shall consider Aquinas' arguments in more detail.

In the 'first way', Aquinas begins by considering motion and that things change. For example, wood is potentially hot. Fire changes wood, and also is potentially cold. Motion is described as that which changes something from what it could be potentially, to that actuality. Yet motion cannot cause itself, and a thing cannot both be moved, and be the mover i.e. things cannot move themselves. From this Aquinas concludes:

... what ever is moved must be moved by another. ( The Five Ways, p. 83).

This process cannot go on backwards forever, one thing being moved by the thing before it, the latter being moved by the thing before it etc. If there were an infinite regress, there would be no first mover, and so no other movers as everything is caused by a first mover. And this first mover, Aquinas says, is God.

Aquinas' 'second way' considers efficient causes. Here Aquinas draws attention to the idea that there is an order of efficient causes, and that one thing is caused to exist by another. He states:

There is no case known (neither is it, indeed, possible) in which a thing is found to be the efficient cause of itself. ( ibid, p. 83).

Aquinas continues, explaining there cannot be an infinite regress of causes, tracing back the existence of a particular thing forever. This, Aquinas says, is impossible because without a first efficient cause, there will not be anything in existence. And so there is a first cause of existence, which Aquinas says is God.

The focus of the 'third way' is on the possibility and necessity of things in nature. Aquinas says things in nature are possible to be and not be; they can be generated or corrupted. These are contingent beings. He thus reasons that:

If everything can not-be, then at one time there was nothing in existence. ( ibid. p. 84).

If this were true, there would be nothing in existence now, as things exist now, and everything in existence now was caused by something in existence all ready. So if everything can not-be at some time, there would be nothing in existence now - which is not true. Aquinas concludes from this, that not all beings are contingent beings; that there are some beings which are necessary beings. He says an infinite regress of necessary beings is impossible, as proven in the 'second way' with regards to efficient causes. So

... we cannot but admit the existence of some being having of itself its own necessity, and not receiving it from another, but rather causing in others their necessity. ( ibid. p. 84).

Aquinas concludes that this necessary being must be God.

The 'fourth way' examines the gradation which is found in things. Here Aquinas focuses on the details in things; that some are better than others, and other things are less so. This is in contrast to one thing which must be the maximum. For example, that which is hotter in comparison to that which is hottest. This he applies also, to qualities such as nobility, perfection, truth. He then quotes a passage from Metaph ii, which claims that the maximum of, say heat, is also the cause of all hot things. He concludes:

Therefore there must also be something which is to all beings the cause of their being, goodness, and every other perfection; and this we call God. ( ibid. p. 85).

The fifth and final proof Aquinas offers for the existence of God stems from the governance of the world. He deduces that things that lack knowledge, that is birds, plants, natural bodies, behave as if with purpose, and achieve, or work toward, certain ends. The natural bodies utilise the best means available to them, and almost always behave in the same way to produce these ends. According to Aquinas, this is evidence of design. For

... whatever lacks knowledge cannot move toward an end, unless it be directed by some being endowed with knowledge and intelligence... ( ibid. p. 85).

Aquinas concludes that there must be an intelligent being who directs all these natural bodies to their end, namely God

How valid and persuasive then are Aquinas' Five Ways 2 . Firstly we need to consider Aquinas' analysis of causes. He assumes there must be a single cause of the universe and also that this must be a first primary cause - which he calls God. But this is only an assumption. Aquinas provides no evidence for this point. It could be argued for example that there may be a multiple number of causes at the beginning? Also there is nothing in his argument to support the claim that an infinite regress of causes is impossible. It could be for example that the world/universe has always been in existence, one thing causing another, evolving constantly according to what has come before? Modern physics offers an alternative explanation of the world along these lines, and suggests that uncaused events are not impossible.

Another point that can be challenged is Aquinas' conclusion at the end of each of the five ways - that the only explanation for the phenomena he discusses is 'God'. Such a conclusion is not likely to convince atheists or those with alternative spiritualities who recognise other beings and deities. If however we accept Aquinas' arguments, on what basis can he be sure about what kind of God it is? Aquinas assumes the God he describes is a fundamentally good one. His reply to the objection that - if God existed there would be no evil in the world - is that God allows evil so as to bring good out of it. But how can we be sure that God's actions, if he exists, are fundamentally good. It could be for example that God is playing tricks on humanity. What if it was a God conducting experiments in world making and universe creating? Who says this existence is perfectly designed? It could be a baby God's first attempt; or two Gods playing chess with their creations. These are all possible alternative explanations - ones that Aquinas does not take up.

We can see in these possibilities that Aquinas' arguments for God's existence and God's fundamental goodness are very much governed by certain religious assumptions that were no doubt held by many at the time. Thus reading his text in the present day, I find his arguments to be quite unconvincing.


  1. St. Thomas Aquinas The Five Ways. In course notes - PHIL 1010 " Science, Religion and Witchcraft".
  2. Some of the following is taken from PHIL 1010 lecture - Graham Oppy
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