Reply to Objection 7. In efficient causes it is impossible to proceed to infinity per se—thus, there cannot be an infinite number of causes that are per se required for a certain effect; for instance, that a stone be moved by a stick, the stick by the hand, and so on to infinity. But it is not impossible to proceed to infinity “accidentally” as regards efficient causes; for instance, if all the causes thus infinitely multiplied should have the order of only one cause, their multiplication being accidental, as an artificer acts by means of many hammers accidentally, because one after the other may be broken. It is accidental, therefore, that one particular hammer acts after the action of another; and likewise it is accidental to this particular man as generator to be generated by another man; for he generates as a man, and not as the son of another man. For all men generating hold one grade in efficient causes—viz. the grade of a particular generator. Hence it is not impossible for a man to be generated by man to infinity; but such a thing would be impossible if the generation of this man depended upon this man, and on an elementary body, and on the sun, and so on to infinity.
Read Article 1, same part…
I answer that, Nothing except God can be eternal. And this statement is far from impossible to uphold: for it has been shown above (I:19:4) that the will of God is the cause of things. Therefore things are necessary, according as it is necessary for God to will them, since the necessity of the effect depends on the necessity of the cause (Metaph. v, text 6). Now it was shown above (I:19:3), that, absolutely speaking, it is not necessary that God should will anything except Himself. It is not therefore necessary for God to will that the world should always exist; but the world exists forasmuch as God wills it to exist, since the being of the world depends on the will of God, as on its cause. It is not therefore necessary for the world to be always; and hence it cannot be proved by demonstration.
From your quote…
But it is not impossible to proceed to infinity “accidentally” as regards efficient causes… What Aquinas seems to be getting at is a kind of
theoretical possibility regarding accidental causation. I.e., that theoretically speaking it is possible to multiply causes to infinity. That does not, however take
time into consideration. Where causes in time (actual causation) are the subject, he appears to
hedge his opinion on the matter.
Continued…