Obj. 5: Further, nothing begins anew to be moved except through either the mover or the thing moved being otherwise than it was before. But what is otherwise now than it was before, is moved. Therefore before every new movement there was a previous movement. Therefore movement always was; and therefore also the thing moved always was, because movement is only in a movable thing.
Obj. 6: Further, every mover is either natural or voluntary. But neither begins to move except by some pre-existing movement. For nature always moves in the same manner: hence unless some change precede either in the nature of the mover, or in the movable thing, there cannot arise from the natural mover a movement which was not there before. And the will, without itself being changed, puts off doing what it proposes to do; but this can be only by some imagined change, at least on the part of time. Thus he who wills to make a house tomorrow, and not today, awaits something which will be tomorrow, but is not today; and at least awaits for today to pass, and for tomorrow to come; and this cannot be without change, because time is the measure of movement. Therefore it remains that before every new movement, there was a previous movement; and so the same conclusion follows as before.
Obj. 7: Further, whatever is always in its beginning, and always in its end, cannot cease and cannot begin; because what begins is not in its end, and what ceases is not in its beginning. But time always is in its beginning and end, because there is no time except "now" which is the end of the past and the beginning of the future. Therefore time cannot begin or end, and consequently neither can movement, the measure of what is time.
Obj. 8: Further, God is before the world either in the order of nature only, or also by duration. If in the order of nature only, therefore, since God is eternal, the world also is eternal. But if God is prior by duration; since what is prior and posterior in duration constitutes time, it follows that time existed before the world, which is impossible.
Obj. 9: Further, if there is a sufficient cause, there is an effect; for a cause to which there is no effect is an imperfect cause, requiring something else to make the effect follow. But God is the sufficient cause of the world; being the final cause, by reason of His goodness, the exemplar cause by reason of His wisdom, and the efficient cause, by reason of His power as appears from the above (Q. 44, AA. 2, 3, 4). Since therefore God is eternal, the world is also eternal.
Obj. 10: Further, eternal action postulates an eternal effect. But the action of God is His substance, which is eternal. Therefore the world is eternal.
On the contrary, It is said (John 17:5), "Glorify Me, O Father, with Thyself with the glory which I had before the world was"; and (Prov. 8:22), "The Lord possessed Me in the beginning of His ways, before He made anything from the beginning."
I answer that, Nothing except God can be eternal. And this statement is far from impossible to uphold: for it has been shown above (Q. 19, A. 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 (Q. 19, A. 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.
Nor are Aristotle's reasons (Phys. viii) simply, but relatively, demonstrative—viz. in order to contradict the reasons of some of the ancients who asserted that the world began to exist in some quite impossible manner. This appears in three ways. Firstly, because, both in Phys. viii and in De Coelo i, text 101, he premises some opinions, as those of Anaxagoras, Empedocles and Plato, and brings forward reasons to refute them. Secondly, because wherever he speaks of this subject, he quotes the testimony of the ancients, which is not the way of a demonstrator, but of one persuading of what is probable. Thirdly, because he expressly says (Topic. i, 9), that there are dialectical problems, about which we have nothing to say from reason, as, "whether the world is eternal."
Reply Obj. 1: Before the world existed it was possible for the world to be, not, indeed, according to a passive power which is matter, but according to the active power of God; and also, according as a thing is called absolutely possible, not in relation to any power, but from the sole habitude of the terms which are not repugnant to each other; in which sense possible is opposed to impossible, as appears from the Philosopher (Metaph. v, text 17).