Reply Obj. 2: Whatever has power always to be, from the fact of having that power, cannot sometimes be and sometimes not be; but before it received that power, it did not exist.
Hence this reason which is given by Aristotle (De Coelo i, text 120) does not prove simply that incorruptible things never began to exist; but that they did not begin by the natural mode whereby things generated and corruptible begin.
Reply Obj. 3: Aristotle (Phys. i, text 82) proves that matter is unbegotten from the fact that it has not a subject from which to derive its existence; and (De Coelo et Mundo i, text 20) he proves that heaven is ungenerated, forasmuch as it has no contrary from which to be generated. Hence it appears that no conclusion follows either way, except that matter and heaven did not begin by generation, as some said, especially about heaven. But we say that matter and heaven were produced into being by creation, as appears above (Q. 44, A. 1, ad 2).
Reply Obj. 4: The notion of a vacuum is not only "in which is nothing," but also implies a space capable of holding a body and in which there is not a body, as appears from Aristotle (Phys. iv, text 60). Whereas we hold that there was no place or space before the world was.
Reply Obj. 5: The first mover was always in the same state: but the first movable thing was not always so, because it began to be whereas hitherto it was not. This, however, was not through change, but by creation, which is not change, as said above (Q. 45, A. 2, ad 2). Hence it is evident that this reason, which Aristotle gives (Phys. viii), is valid against those who admitted the existence of eternal movable things, but not eternal movement, as appears from the opinions of Anaxagoras and Empedocles. But we hold that from the moment that movable things began to exist movement also existed.
Reply Obj. 6: The first agent is a voluntary agent. And although He had the eternal will to produce some effect, yet He did not produce an eternal effect. Nor is it necessary for some change to be presupposed, not even on account of imaginary time. For we must take into consideration the difference between a particular agent, that presupposes something and produces something else, and the universal agent, who produces the whole. The particular agent produces the form, and presupposes the matter; and hence it is necessary that it introduce the form in due proportion into a suitable matter. Hence it is correct to say that it introduces the form into such matter, and not into another, on account of the different kinds of matter. But it is not correct to say so of God Who produces form and matter together: whereas it is correct to say of Him that He produces matter fitting to the form and to the end. Now, a particular agent presupposes time just as it presupposes matter. Hence it is correctly described as acting in time "after" and not in time "before," according to an imaginary succession of time after time. But the universal agent who produces the thing and time also, is not correctly described as acting now, and not before, according to an imaginary succession of time succeeding time, as if time were presupposed to His action; but He must be considered as giving time to His effect as much as and when He willed, and according to what was fitting to demonstrate His power. For the world leads more evidently to the knowledge of the divine creating power, if it was not always, than if it had always been; since everything which was not always manifestly has a cause; whereas this is not so manifest of what always was.
Reply Obj. 7: As is stated (Phys. iv, text 99), "before" and "after" belong to time, according as they are in movement. Hence beginning and end in time must be taken in the same way as in movement. Now, granted the eternity of movement, it is necessary that any given moment in movement be a beginning and an end of movement; which need not be if movement be a beginning. The same applies to the "now" of time. Thus it appears that the idea of the instant "now," as being always the beginning and end of time, presupposes the eternity of time and movement. Hence Aristotle brings forward this reason (Phys. viii, text 10) against those who asserted the eternity of time, but denied the eternity of movement.
Reply Obj. 8: God is prior to the world by priority of duration. But the word "prior" signifies priority not of time, but of eternity. Or we may say that it signifies the eternity of imaginary time, and not of time really existing; thus, when we say that above heaven there is nothing, the word "above" signifies only an imaginary place, according as it is possible to imagine other dimensions beyond those of the heavenly body.
Reply Obj. 9: As the effect follows from the cause that acts by nature, according to the mode of its form, so likewise it follows from the voluntary agent, according to the form preconceived and determined by the agent, as appears from what was said above (Q. 19, A. 4; Q. 41, A. 2). Therefore, although God was from eternity the sufficient cause of the world, we should not say that the world was produced by Him, except as preordained by His will—that is, that it should have being after not being, in order more manifestly to declare its author.
Reply Obj. 10: Given the action, the effect follows according to the requirement of the form, which is the principle of action. But in agents acting by will, what is conceived and preordained is to be taken as the form, which is the principle of action. Therefore from the eternal action of God an eternal effect did not follow; but such an effect as God willed, an effect, to wit, which has being after not being. _______________________