St. Thomas Aquinas, De Aeternitate Mundi (On the Eternity of the World). Translation 1991, 1997 by Robert T. Miller.*

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Let us assume, in accordance with the Catholic faith, that the world had a beginning in time. The question still arises whether the world could have always existed, and to explain the truth of this matter, we should first distinguish where we agree with our opponents from where we disagree with them. If someone holds that something besides God could have always existed, in the sense that there could be something always existing and yet not made by God, then we differ with him: such an abominable error is contrary not only to the faith but also to the teachings of the philosophers, who confess and prove that everything that in any way exists cannot exist unless it be caused by him who supremely and most truly has existence. However, someone may hold that there has always existed something that, nevertheless, had been wholly caused by God, and thus we ought to determine whether this position is tenable.

If it be impossible that something caused by God has always existed, it will be so either because God could not make something that has always existed or because such a thing could not be made, regardless of God's ability to make it. As to the first, all parties agree that, in view of his infinite power, God could have made something that has always existed. It remains to be seen, therefore, whether something that has always existed can be made.

If such a thing cannot be made, the impossibility will arise for one of two reasons: either because of an absence of a passive potentiality or because of some contradiction between the ideas involved. In regard to the first, notice that before an angel is made, we may say, in a certain manner of speaking, that the angel cannot be made, since no passive potentiality precedes its being, for an angel is not made from pre-existing matter. Nevertheless, God was able to make the angel, and he was able to cause the angel to be made, for God made it, and it was made. Therefore, if we understand "being made" or "being caused" as implying the pre-existence of a passive potentiality, then it should to be conceded, according to faith, that something caused cannot always exist, for it would then follow that a passive potentiality has always existed, and this is heretical. But since a passive potentiality need not precede in time whatever God may make, it does not follow that God could not have made something that has always existed.

In regard to the second, someone may hold that something that has always existed cannot be made because such a thing is self-contradictory, just as an affirmation and a denial cannot be made simultaneously true. Still, some people say that God can even make self-contradictories things, while others say God cannot make such things, for such things are actually nothing. Clearly, God cannot make such things come to be, for the assumption that such a thing exists immediately refutes itself. Nevertheless, if we allow that God can make such things come to be, the position is not heretical, though I believe it is false, just as the proposition that the past did not occur is false, about which Augustine says (XXVI Contra Faustum cap. 5), "Anyone who says, 'If God is omnipotent, let him make what has happened not to have happened,' does not realize that he is saying, 'If God is omnipotent, let him make true things false insofar as they are true.'" [PL 42, 481.] Nevertheless, certain great men have piously maintained that God can make past events not to have happened, and this was not reputed to be heretical.

We thus ought to determine whether there is any contradiction between these two ideas, namely, to be made by God and to have always existed. And, whatever may be the truth of this matter, it will not be heretical to say that God can make something created by him to have always existed, though I believe that if there were a contradiction involved in asserting this, the assertion would be false. However, if there is no contradiction involved, then it is neither false nor impossible that God could have made something that has always existed, and it will be an error to say otherwise. For, if there is no contradiction, we ought to admit that God could have made something that has always existed, for it would be clearly derogatory to the divine omnipotence, which exceeds every thought and power, to say that we creatures can conceive of something that God is unable to make. (Nor are sins an instance to the contrary, for, considered in themselves, they are nothing.) In this, therefore, the entire question consists: whether to be wholly created by God and not to have a beginning in time are contradictory terms.

That they are not contradictory can be shown as follows. If they are contradictory, this is for one or both of these two reasons: either because the agent cause must precede the effect in time, or because non-being must precede the effect in time, for we say that what God creates comes to be out of nothing.

First, we should show that it is not necessary that an agent cause, in this case God, precede in time that which he causes, if he should so will. This can be shown in several ways. First, no cause instantaneously producing its effect necessarily precedes the effect in time. God, however, is a cause that produces effects not through motion but instantaneously. Therefore, it is not necessary that he precede his effects in time. The first premise is proved inductively from all instantaneous changes, as, for example, with illumination and other such things. But the premise may be proved by reason as well.

For, at whatever instant a thing exists, at that instant it can begin to act, as is clear in the case of all things that come to be by generation: in the very instant at which there is fire, the fire heats. But in an instantaneous action, the beginning and the end of the action are simultaneous, indeed identical, as is clear in the case of all indivisible things. Hence, at whatever moment an agent instantaneously producing an effect exists, the end of its action can exist as well. The end of the action, however, is simultaneous with the thing made. Therefore, there is no contradiction if we suppose that a cause instantaneously producing an effect does not precede its effect in time. A contradiction does obtain if the cause involved is one that produces its effects through motion, for the beginning of the motion precedes in time the end of the motion. Since people are accustomed to considering the type of cause that produces effects through motion, they do not easily grasp that an agent cause may fail to precede its effect in time, and so, having limited experience, they easily make a false generalization.

Nor can the conclusion be avoided by saying that God is an agent cause that acts voluntarily, for neither the will nor the voluntary agent need precede its effect in time, unless the agent cause acts from deliberation, which we take to be absent in God.

Further, a cause that produces the whole substance of a thing does not, in producing a whole substance, act in a less perfect way than does a cause that produces just a form in producing the form. On the contrary, it acts in a much more perfect way, since it does not act by educing from the potentiality of matter, as do causes that merely produce forms. However, some causes that produce just forms are such that, whenever the cause exists, the form produced by it exists as well, as is clear in the case of illumination by the sun. Therefore, much more can God, who produces the whole substance of things, make something caused by him exist whenever he himself exists.

Further, if, granted a cause, its effect does not immediately exist as well, this can only be because something complementary to that cause is lacking: the complete cause and the thing caused are simultaneous. God, however, never lacks any kind of complementary cause in order to produce an effect. Therefore, at any instant at which God exists, so too can his effects, and thus God need not precede his effects in time.

Further, the will of the voluntary agent in no way diminishes his power, and this is especially true with God. But all those who try to answer the arguments of Aristotle (who held that something caused by God had always existed, since like always makes like) say that the conclusion would follow if God were not a voluntary agent. Therefore, allowing that God is a voluntary agent, it still follows that he can make something that he has made never fail to exist. Thus, although God cannot make contradictories true, we have shown that there is no contradiction in saying that an agent cause does not precede its effect in time.

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