Summa contra Gentiles2.36 Chapter XXXVI. Solution of the arguments produced on the part of the things made

In like manner again, neither is there, on the part of creatures, anything to induce us to assert their eternity.

For the necessity of being that we find in creatures, from which the first argument is taken, is a necessity of order, as was shown above: and a necessity of order does not compel the subject of a like necessity to have been always, as we proved above. For although the substance of heaven, through being devoid of potentiality to non-being, has a potentiality to being, yet this necessity follows its substance. Wherefore its substance once brought into being, this necessity involves the impossibility of not being: but it does not make it impossible for the heaven not to be, from the point of view where we consider the production of its very substance.

Likewise the power to be always, from which the second argument proceeded, presupposes the production of the substance. Hence where the production of the heaven’s substance is in question, this power cannot be a sufficient argument for that substance’s eternity.

Again, the argument adduced in sequence does not compel us to admit the eternity of movement. For it has been made clear that without any change in God the agent, it is possible for Him to do something new that is not eternal. And if it is possible for something to be done by Him anew, it is evident that something can also be moved by Him anew: since newness of movement is consequent upon the ordinance of the eternal will to the effect that movement be not always.

Likewise the intention which natural agents have of perpetuating the species, which was the starting point of the fourth argument, presupposes that natural agents are already in being. Wherefore this argument has no place, save in natural things already brought into being, but not when it is a question of the (first) production of things. The question as to whether it is necessary to admit that generation will go on for ever will be discussed in the sequel.

Also the fifth argument, taken from time, supposes rather than proves the eternity of movement. For since before and after and continuity of time are consequent upon before and after and continuity of movement, according to the teaching of Aristotle, it is clear that the same instant is the beginning of the future, and the end of the past, because in movement there is something assignable that is the beginning and end of the various parts of movement. Wherefore it will not be necessary for each instant to be thus, unless every assignable instant that we conceive in time be between before and after in movement, and this is to suppose that movement is eternal. But he who supposes that movement is not eternal, can say that the first instant of time is the beginning of the future, and the end of no past. Nor is it incompatible with the succession of time, if we place therein a now that is a beginning and not an end, because a line in which we place a point that is a beginning and not an end, is stationary and not transitory; since even in a particular movement which also is not stationary but transitory, it is possible to designate something as only a beginning and not an end of movement: for otherwise all movement would be perpetual, which is impossible.

That we suppose the non-being of time to precede its being, if time began, does not compel us to say that time is, if we suppose that it is not, as the sixth argument inferred. For the before that we speak of as being before time was, does not imply any part of time in reality but only in our imagination. Because when we say that time has being after non-being, we mean that there was no part of time before this signate now: thus, when we say that there is nothing above the heaven, we do not mean that there is a place outside the heaven which can be said to be above in relation to the heaven, but that there is no place above it. In either case the imagination can apply a measure to the already existing thing: and just as this measure is no reason for admitting infinite quantity in a body, as stated in 3 Phys., so neither is it a reason for supposing that time is eternal.

The truth of propositions which one has to grant even if one denies them, and from which the seventh argument proceeded, has the necessity of that relation which is between predicate and subject. Wherefore it does not compel a thing to be always: except perhaps (as understood by) the divine intellect in which all truth is rooted, as we showed in the First Book.

Hence it is clear that the arguments taken from creatures do not compel one to assert the eternity of the world.