This is a follow-up to Russell’s guest post about Aquinas’ Five Ways. Following a vigorous discussion in the comments, he wanted to clarify his commentary of the Third Way.

My apologies, I’ve muddled up the Third Way a bit here. Let me try it again and unmuddle. If you aren’t satisfied, I’ll double your money back.

The Third Way

The third way is taken from possibility and necessity, and runs thus. We find in nature things that are possible to be and not to be, since they are found to be generated, and to corrupt, and consequently, they are possible to be and not to be. But it is impossible for these always to exist, for that which is possible not to be at some time is not. Therefore, if everything is possible not to be, then at one time there could have been nothing in existence. Now if this were true, even now there would be nothing in existence, because that which does not exist only begins to exist by something already existing. Therefore, if at one time nothing was in existence, it would have been impossible for anything to have begun to exist; and thus even now nothing would be in existence – which is absurd. Therefore, not all beings are merely possible, but there must exist something the existence of which is necessary. But every necessary thing either has its necessity caused by another, or not. Now it is impossible to go on to infinity in necessary things which have their necessity caused by another, as has been already proved in regard to efficient causes. Therefore we cannot but postulate the existence of some being having of itself its own necessity, and not receiving it from another, but rather causing in others their necessity. This all men speak of as God.

The words ‘possibility’ and ‘necessity’ have be used in the context of Aquinas’ time.

‘Possibility’ is used in the Aristotelian sense, that is, the hylemorphic composite nature of something that can possibly be and not to be. This nature is inherent. Whatever form something has now, if it has hylemorphic nature, it will fail to exist in that form given enough time. It lacks the potential for indefinite existence.

By ‘necessity,’ he means the opposite of possibility: something that by its nature is everlasting, it cannot cease to exist no matter how much time passes. It cannot change into something it is not. By its very nature, for example, it cannot become contingent.

Aquinas’ argument starts with establishing the fact that if the hylemorphic somethings of the Universe, be it an entity or an action or a cause or an event or whatever, at some point, given infinite time, never existed, and, again, given infinite time, all things would have never existed, and we wouldn’t be here arguing about why we are here.

He says that’s absurd, and, because we are here, something has to have Necessary Being, which means something that exists is non-temporal and non-contingent. Here he uses being to mean being as existence and as a supreme being that men call God, “I am that I am,” which is of itself Being. He uses being not as one being among other beings, but being qua being. I’m not an expert in Latin, but the tricky passage is here: Ergo necesse est ponere aliquid quod sit per se necessarium, non habens causam necessitatis aliunde, sed quod est causa necessitatis aliis, quod omnes dicunt Deum. Sit per se isn’t complete by itself, so we have to look at necessarium, as well, and that all roughly translates into being as an abstract which has its own necessity, its own everlastingness.

It’s this Necessary Being that sustains all Possible things.

So, Aquinas’ argument then takes care of the Universe always existing, the Universe contracting and expanding forever, and multi-universes for the same reason.

I hope this has unmuddled what I had muddled. Amateur philosophers, sheesh!

Another point is that these Ways are not empirical, scientific proofs, but metaphysical demonstrations. That means none of his arguments are tied to past, current, or future scientific knowledge, because they don’t rest on empirical evidence.