Thomas Aquinas - Summa Theologica, Part I (Prima Pars)

Reply Obj. 3: Necessary means a certain mode of truth; and truth, according to the Philosopher (Metaph. vi), is in the mind. Therefore in this sense the true and necessary are eternal, because they are in the eternal mind, which is the divine intellect alone; hence it does not follow that anything beside God is eternal. ______________________

FOURTH ARTICLE [I. Q. 10, Art. 4]

Whether Eternity Differs from Time?

Objection 1: It seems that eternity does not differ from time. For two measures of duration cannot exist together, unless one is part of the other; for instance two days or two hours cannot be together; nevertheless, we may say that a day or an hour are together, considering hour as part of a day. But eternity and time occur together, each of which imports a certain measure of duration. Since therefore eternity is not a part of time, forasmuch as eternity exceeds time, and includes it, it seems that time is a part of eternity, and is not a different thing from eternity.

Obj. 2: Further, according to the Philosopher (Phys. iv), the "now" of time remains the same in the whole of time. But the nature of eternity seems to be that it is the same indivisible thing in the whole space of time. Therefore eternity is the "now" of time. But the "now" of time is not substantially different from time. Therefore eternity is not substantially different from time.

Obj. 3: Further, as the measure of the first movement is the measure of every movement, as said in Phys. iv, it thus appears that the measure of the first being is that of every being. But eternity is the measure of the first being—that is, of the divine being. Therefore eternity is the measure of every being. But the being of things corruptible is measured by time. Time therefore is either eternity or is a part of eternity.

On the contrary, Eternity is simultaneously whole. But time has a "before" and an "after." Therefore time and eternity are not the same thing.

I answer that, It is manifest that time and eternity are not the same. Some have founded this difference on the fact that eternity has neither beginning nor an end; whereas time has a beginning and an end. This, however, makes a merely accidental, and not an absolute difference because, granted that time always was and always will be, according to the idea of those who think the movement of the heavens goes on for ever, there would yet remain a difference between eternity and time, as Boethius says (De Consol. v), arising from the fact that eternity is simultaneously whole; which cannot be applied to time: for eternity is the measure of a permanent being; while time is a measure of movement. Supposing, however, that the aforesaid difference be considered on the part of the things measured, and not as regards the measures, then there is some reason for it, inasmuch as that alone is measured by time which has beginning and end in time. Hence, if the movement of the heavens lasted always, time would not be of its measure as regards the whole of its duration, since the infinite is not measurable; but it would be the measure of that part of its revolution which has beginning and end in time.

Another reason for the same can be taken from these measures in themselves, if we consider the end and the beginning as potentialities; because, granted also that time always goes on, yet it is possible to note in time both the beginning and the end, by considering its parts: thus we speak of the beginning and the end of a day or of a year; which cannot be applied to eternity. Still these differences follow upon the essential and primary differences, that eternity is simultaneously whole, but that time is not so.

Reply Obj. 1: Such a reason would be a valid one if time and eternity were the same kind of measure; but this is seen not to be the case when we consider those things of which the respective measures are time and eternity.

Reply Obj. 2: The "now" of time is the same as regards its subject in the whole course of time, but it differs in aspect; for inasmuch as time corresponds to movement, its "now" corresponds to what is movable; and the thing movable has the same one subject in all time, but differs in aspect a being here and there; and such alteration is movement. Likewise the flow of the "now" as alternating in aspect is time. But eternity remains the same according to both subject and aspect; and hence eternity is not the same as the "now" of time.

Reply Obj. 3: As eternity is the proper measure of permanent being, so time is the proper measure of movement; and hence, according as any being recedes from permanence of being, and is subject to change, it recedes from eternity, and is subject to time. Therefore the being of things corruptible, because it is changeable, is not measured by eternity, but by time; for time measures not only things actually changed, but also things changeable; hence it not only measures movement but it also measures repose, which belongs to whatever is naturally movable, but is not actually in motion. _______________________

FIFTH ARTICLE [I, Q. 10, Art. 5]

The Difference of Aeviternity and Time

Objection 1: It seems that aeviternity is the same as time. For Augustine says (Gen. ad lit. viii, 20, 22, 23), that "God moves the spiritual through time." But aeviternity is said to be the measure of spiritual substances. Therefore time is the same as aeviternity.

Obj. 2: Further, it is essential to time to have "before" and "after"; but it is essential to eternity to be simultaneously whole, as was shown above in the first article. Now aeviternity is not eternity; for it is written (Ecclus. 1:1) that eternal "Wisdom is before age." Therefore it is not simultaneously whole but has "before" and "after"; and thus it is the same as time.

Obj. 3: Further, if there is no "before" and "after" in aeviternity, it follows that in aeviternal things there is no difference between being, having been, or going to be. Since then it is impossible for aeviternal things not to have been, it follows that it is impossible for them not to be in the future; which is false, since God can reduce them to nothing.

Obj. 4: Further, since the duration of aeviternal things is infinite as to subsequent duration, if aeviternity is simultaneously whole, it follows that some creature is actually infinite; which is impossible. Therefore aeviternity does not differ from time.

On the contrary, Boethius says (De Consol. iii) "Who commandest time to be separate from aeviternity."

I answer that, Aeviternity differs from time, and from eternity, as the mean between them both. This difference is explained by some to consist in the fact that eternity has neither beginning nor end, aeviternity, a beginning but no end, and time both beginning and end. This difference, however, is but an accidental one, as was shown above, in the preceding article; because even if aeviternal things had always been, and would always be, as some think, and even if they might sometimes fail to be, which is possible to God to allow; even granted this, aeviternity would still be distinguished from eternity, and from time.

Others assign the difference between these three to consist in the fact that eternity has no "before" and "after"; but that time has both, together with innovation and veteration; and that aeviternity has "before" and "after" without innovation and veteration. This theory, however, involves a contradiction; which manifestly appears if innovation and veteration be referred to the measure itself. For since "before" and "after" of duration cannot exist together, if aeviternity has "before" and "after," it must follow that with the receding of the first part of aeviternity, the after part of aeviternity must newly appear; and thus innovation would occur in aeviternity itself, as it does in time. And if they be referred to the things measured, even then an incongruity would follow. For a thing which exists in time grows old with time, because it has a changeable existence, and from the changeableness of a thing measured, there follows "before" and "after" in the measure, as is clear from Physic. iv. Therefore the fact that an aeviternal thing is neither inveterate, nor subject to innovation, comes from its changelessness; and consequently its measure does not contain "before" and "after." We say then that since eternity is the measure of a permanent being, in so far as anything recedes from permanence of being, it recedes from eternity. Now some things recede from permanence of being, so that their being is subject to change, or consists in change; and these things are measured by time, as are all movements, and also the being of all things corruptible. But others recede less from permanence of being, forasmuch as their being neither consists in change, nor is the subject of change; nevertheless they have change annexed to them either actually or potentially. This appears in the heavenly bodies, the substantial being of which is unchangeable; and yet with unchangeable being they have changeableness of place. The same applies to the angels, who have an unchangeable being as regards their nature with changeableness as regards choice; moreover they have changeableness of intelligence, of affections and of places in their own degree. Therefore these are measured by aeviternity which is a mean between eternity and time. But the being that is measured by eternity is not changeable, nor is it annexed to change. In this way time has "before" and "after"; aeviternity in itself has no "before" and "after," which can, however, be annexed to it; while eternity has neither "before" nor "after," nor is it compatible with such at all.