THIRD PROOF: FROM THE CONTINGENCY OF BEINGS IN THE WORLD

There are beings in the world which are evidently contingent, that is to say, they can exist or not exist. Thus plants and animals live and die, and science assures us that there was a time when there were neither plants nor animals, nor men on this earth, and when the stars were not as they are to-day, but in a nebulous state.

Now, contingent beings presuppose a necessary and self-existing being. What is contingent has not its own raison d’être within itself, nor is it the cause of its own existence. Therefore, there must be some necessary being. Moreover, if the necessity of this being or principle is merely relative (for instance, limited from the physical point of view, so as to account for the physico-chemical phenomena of the lower order), then we must continue our inquiry, until we arrive at an absolutely necessary being; for, as we have seen, we cannot proceed ad infinitum in a series of causes which are essentially subordinated one to another. Consequently, there must be an absolutely necessary Being, the cause of all the others.

Ia, q. 44, a. 1.

a) This necessary Being is not the sum-total of contingent beings, even if this series were infinite in space and time; for we may go on increasing the number of contingent beings, but they will always be contingent, and can no more constitute a necessary being, than a countless number of idiots can constitute an intelligent man.

b) Neither is the necessary Being the law of contingent beings, since this law depends for its existence upon the existence of contingent beings.

c) Finally, the necessary Being is not a substance common to all phenomena; for this substance would be subject to motion (see First Proof), and would receive determinations or new perfections, which it could not have produced itself, since the greater cannot come from the less. The necessary Being can certainly give, but it cannot receive; it can determine, but it cannot be determined. It has of itself and from all eternity, all that it can have.

Ia, q. 3, a. 6.

Moreover, from the fact that the necessary Being is self-existent, it follows that its essence is not merely a capacity to exist—which capacity receives and limits existence—but it is unreceived or subsistent existence, self-subsisting Being.

Ia, q. 3, a. 4; q. 7, a. 1.