Summa contra Gentiles2.33 Chapter XXXIII. Arguments of those who would prove the eternity of the world from the point of view of creatures

There are also other arguments, taken from the point of view of creatures, that would seem to prove the same conclusion.

For things which have no potentiality to non-being, cannot possibly not be. Now there are some creatures in which there is no potentiality to non-being. For there cannot be potentiality to non-being except in those things which have matter subject to contrariety: since potentiality to being and to non-being is a potentiality to privation and form, of which matter is the subject; and privation is always connected with the opposite form, since it is impossible for matter to be without any form at all. But there are certain creatures in which the matter is not subject to contrariety: either because they are entirely devoid of matter; for instance intellectual substances, as we shall show further on, or because they have no contrary, as heavenly bodies, and this is proved by their movement, 2 De A nima, iv. 2. 2 which has no contrary. Therefore it is impossible for certain creatures not to exist: and consequently it is necessary that they exist always.

Again. A thing’s endurance in being is in proportion to its power of being, except accidentally, as in those which are corrupted by violence. But there are certain creatures in which there is a power of being not for any definite time, but for ever; for instance the heavenly bodies and intellectual substances, because they are incorruptible through having no contrary. It follows, then, that it is competent to them to be always. But that which begins to exist, is not always. Therefore it is not becoming to them that they begin to exist.

Further. Whenever a thing begins to be moved anew, the mover, or the moved, or both, must be conditioned otherwise now while the movement is, than before when there was no movement: for there is a certain habitude or relation in the mover to the thing moved, for as much as it moves actually; and the new relation does not begin without a change either in both or at least in one or other of the extremes. Now that which is conditioned otherwise now and heretofore, is moved. Therefore, before the movement that begins anew, there must be a previous movement either in the movable or in the mover. It follows, in consequence, that every movement is either eternal, or has another movement preceding it. Therefore movement always has been; and consequently movable also. Therefore there have alw’ays been creatures: since God is utterly immovable, as we proved in the First Book.

Further. Every agent that engenders its like, intends to preserve perpetual being in the species, for it cannot be preserved perpetually in the individual. But it is impossible for the desire of nature to be frustrated. Therefore it follows that the species of generable things are everlasting.

Again. If time is everlasting, movement must be everlasting, since it is the reckoning of movement and consequently movables must be everlasting, since movement is the act of a movable. Now time must needs be perpetual. For time is inconceivable without a now: even as a line is' inconceivable without a point. But now is always the end of the past and the beginning of the future, for this is the definition of the now. Wherefore every given now has time preceding it and following it; and consequently no now can be either first or last. It follows therefore that movables which are created substances are from eternity.

Again. One must either affirm or deny. If, therefore, by denying a thing we suppose its existence, that thing must needs be always. Now time is a thing of this kind. For if time was not always, we can conceive it as not being previously to being: and in like manner, if it will not be always, its non-being must follow its being. Now there can be no before and after in duration unless there be time; since the reckoning of before and after is time. Consequently time must have been before it began to be, and will be after it has ceased to be: and therefore time is eternal. But time is an accident: and an accident cannot be without a subject. And its subject is not God, Who is above time; since He is utterly immovable, as we proved in the First Book. Therefore it follows that some created substance is eternal.

Moreover. Many propositions are such that to deny them is to affirm them: for instance whoso denies that truth exists, supposes the existence of truth, for he supposes that the denial which he utters is true. It is the same with one who denies this principle that contradictories are not simultaneous: since by denying this he asserts that the negative which he utters is true, and that the opposite affirmative is false, and thus that both are not true about the same thing. Accordingly if, as we have proved, a thing which through being denied has to be admitted, must be always, it follows that the aforesaid propositions, and all that result from them, are everlasting. But such propositions are not God. Therefore something beside God must be eternal.

These, then, and similar arguments may be taken from the standpoint of creatures to prove that creatures have been always.