Argument for the existence of God from the existence of immaterial souls

[Matteo97]

There is a famous argument, endorsed by many catholic philosophers (St. Alphonse Liguori to name one) which aims to prove the existence of God from the existence of (human) immaterial souls. I understand how to rule out the possibility of the creation of immaterial souls from matter (by principle of proportionate causality) however, I don't understand how to rule out the possibility of an infinite regress of immaterial souls causing the existence of another or the possibility of a non-divine immaterial soul existing from eternity.

I'm sorry, I've already submitted this topic. How can I eliminate this duplicate?

[LittleDiana]

Let me try...

Are you familiar with the theory of potency and act, and with the five ways of Aquinas?

Every human being (and every contingent being) is composed of essence and being. The essence is potency; a potency, to become in act needs another act to produce that change. This last act, in turn needed the influx of another act and so on. But it is impossible to have an infinite chain of things that cause and are caused; then, you need something that causes without being caused, and that is what we call God. The  point here is to think it not chronologically but ontologically. I mean: I needed my parents in order to come into existence, and for them to exist it was necessary that my grandparents existed before and so on; but the existence of my parents here and now is not conditioned by that of my grandparents. If my grandparents die, my parents would still be alive.

The same goes with the second case. As long as that being is not divine, it is not Being itself; if it is not being itself it has an essence; and if it has an essence then it is potencial and needs the pure act of Being (God) to exist.

This was an important philosophical discussion in the time of Aquinas, because some arabic philosophers, following other greek philosophers, said that the world was eternal, which we know by faith isn't true. The proposition was seen as somehow atheistic: if the world exists from eternity then it wasn't created. Aquinas argued that even if the world was eternal, it needed God conservate into being, and to create and to conservate into being are the same operation.

Steven Baldner and William Carroll in "Aquinas on creation" did a very good translation of a commentary of Aquinas in which he addresses this topic. Their introduction is clear and complete. I recommend it if you want a more precise and detailed answer.