The ways of Aquinas

Carolin asked:

Hi, I wonder what the steps for Aquinas’ Causal Argument for the Existence of God are. Thank you.

Answer by Martin Jenkins

In his ‘Summa Theologiae’, Aquinas posits his proofs for the existence of the Christian God as the ‘Five Ways’.

The first argument is the argument from Motion. It can be observed that things in the world are in motion. A thing in motion does not cause itself to move or be sui generis (this prevails only if one remains within the categories of Aristotelian metaphysics where a thing cannot be both actus and potentia at the same moment) but is caused to motion by some other thing. Whilst the potential for motion lies within the thing B, its actual motion must arise from some prior existing thing A actually in motion, which actualises the potential inherent in B.

This leads to an infinite regress in which there is no first mover. If there is no first mover then ‘there would not be a first mover and consequently, any other mover’. To avoid this argument from absurdity, there must be a First mover which is itself, not moved by anything. This first mover is God.

However, why does Aquinas, in this argument, find it objectionable that motion is infinite? Could he be accused assuming the truth of that which has yet to be proved, (Peticio Principi) as it is equally possible that motion has always existed?

The Second Argument is that from Efficient Cause. Again, the senses perceive a series of Efficient causes (i.e. A causes B, B causes C and so on) in the world. A thing cannot cause itself into existence (causa sui), it would have to exist before it exists so as to cause its own existence — which is impossible. So things, as effects, are caused into existence by a prior existing efficient cause. So there is a series of Efficient causes in the world. However, an infinite regress of efficient causes is impossible because a regress rules out a first cause and without a first cause, there would not be a subsequent effect and so, nothing would exist – which is absurd. So there cannot be an infinite regress and there must be a First cause of the series of efficient causes and this, is God.

Again, it is equally possible that there was no first cause and that what exists has always existed. Pace Spinoza…

The Third Argument is based on Possibility and Necessity. Things both exist and cease to exist, are generated and destroyed. If every thing was like this, then not existing is possible. If everything is such that not existing is possible for it, then at some time there was nothing in existence. But if nothing existed in the past, there would be nothing presently in existence for, from nothing comes nothing (ex nihilo nihil fit). Yet this is false, as we are here answering this question. Thus it is not true that all things exist possibly. There must be beings which necessarily exist. Some beings exist necessarily because they were caused to exist by other beings. But the problem of infinite regress applies here as it does in the Second Argument. So, there must be a being which exists by necessity and is not caused to exist by anything else. This being is God.

The fallacy committed here is in the drawing of the conclusion that nothing exists follows on from the fact that contingent beings exist. For whist some beings might not exist at any given time, others do exist. Possible existence does not give rise to the impossibility of existence — an erroneous position which then invites the need for a necessary being — God.

The Forth Argument is based on the degrees of reality or eminence found in existing things. That is, things display different quantitative levels in relation to an optimum. There are varying levels of existence, goodness and perfection in living things. God as the maximum epitome of existence, goodness and perfection is the cause of such things.

This line of argument is found in Aristotle’s ‘Metaphysics’. It argues that the cause of an effect must have sufficient perfection and reality to cause such effects and that the cause is present in those effects in a sliding scale of greater or lesser degree in relation to the cause itself.

The Final and Fifth Argument is a nascent Argument from Design/Teleology as a proof for the existence of God. Again, like all of the arguments in the Five Ways, it has its origin in Aristotle’s Metaphysics. Non-thinking things can be observed to act in a purposive, directed way which, is always for the best outcome. It is not by chance that they act like this. If not by chance, it is because there is an intelligent being which directs non-thinking beings toward their ends (telos). The intelligent being is God.

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