Thomas Aquinas’ Cosmological Argument for the Existence of God

The venerable priest’s argument, roughly, is that:

Everything that exists has a cause. Therefore there must be an uncaused first cause, and that is God.

His premise (or reason) is that:

Everything that exists has a cause.

(There is, I’m sure, no ambiguity in the definition of “everything that exists.”)

While it would be of little consequence to argue about the truth of Aquinas’ premise (does everything really have a cause?), the argument falls short of the second condition for soundness of an argument in that his conclusion (there must be an uncaused first cause, God) does not follow logically, from his premise. In other words, his premise (everything that exists has a cause) does not lead, logically, to his conclusion.

In fact, Aquinas’ own conclusion seems to be the anti-thesis of the logical conclusion that proceeds from his premise. If he bases his argument on the premise that everything that exists has a cause, and we agree that God does exist, then it follows, contrary to his own inference, that God does, indeed, have a cause.

As a matter of fact, Aquinas’ premise would serve the argument of an atheist better:

Everything that exists has a cause. Therefore causes and effects go on indefinitely: an effect has a cause, and that cause has a cause, and that cause has a cause, indefinitely.

The atheist might even further the preceding argument thus:

Since causes and effects go on indefinitely, God has a cause, and that cause has a cause, and that cause has a cause, indefinitely.

The problem with Aquinas’ Cosmological Argument for the Existence of God, then, is that it fails to meet the second condition for a sound argument (Validity of Inference): his conclusion does not follow logically from his premise.

20 July 2003