Objection 2: Further, what is before eternity, and after eternity, is not measured by eternity. But, as Aristotle says (De Causis), "God is before eternity and He is after eternity": for it is written that "the Lord shall reign for eternity, and beyond [*Douay: 'for ever and ever']" ( Ex. 15:18 ). Therefore to be eternal does not belong to God.
Objection 3: Further, eternity is a kind of measure. But to be measured belongs not to God. Therefore it does not belong to Him to be eternal.
Objection 4: Further, in eternity, there is no present, past or future, since it is simultaneously whole; as was said in the preceding article. But words denoting present, past and future time are applied to God in Scripture. Therefore God is not eternal.
On the contrary, Athanasius says in his Creed: "The Father is eternal, the Son is eternal, the Holy Ghost is eternal."
I answer that, The idea of eternity follows immutability, as the idea of time follows movement, as appears from the preceding article. Hence, as God is supremely immutable, it supremely belongs to Him to be eternal. Nor is He eternal only; but He is His own eternity; whereas, no other being is its own duration, as no other is its own being. Now God is His own uniform being; and hence as He is His own essence, so He is His own eternity.
Reply to Objection 1: The "now" that stands still, is said to make eternity according to our apprehension. As the apprehension of time is caused in us by the fact that we apprehend the flow of the "now," so the apprehension of eternity is caused in us by our apprehending the "now" standing still. When Augustine says that "God is the author of eternity," this is to be understood of participated eternity. For God communicates His eternity to some in the same way as He communicates His immutability.
Reply to Objection 2: From this appears the answer to the Second Objection. For God is said to be before eternity, according as it is shared by immaterial substances. Hence, also, in the same book, it is said that "intelligence is equal to eternity." In the words of Exodus, "The Lord shall reign for eternity, and beyond," eternity stands for age, as another rendering has it. Thus it is said that the Lord will reign beyond eternity, inasmuch as He endures beyond every age, i.e. beyond every kind of duration. For age is nothing more than the period of each thing, as is said in the book De Coelo i. Or to reign beyond eternity can be taken to mean that if any other thing were conceived to exist for ever, as the movement of the heavens according to some philosophers, then God would still reign beyond, inasmuch as His reign is simultaneously whole.
Reply to Objection 3: Eternity is nothing else but God Himself. Hence God is not called eternal, as if He were in any way measured; but the idea of measurement is there taken according to the apprehension of our mind alone.
Reply to Objection 4: Words denoting different times are applied to God, because His eternity includes all times; not as if He Himself were altered through present, past and future.
Whether to be eternal belongs to God alone?
Objection 1: It seems that it does not belong to God alone to be eternal. For it is written that "those who instruct many to justice," shall be "as stars unto perpetual eternities [*Douay: 'for all eternity']" ( Dan. 12:3 ). Now if God alone were eternal, there could not be many eternities. Therefore God alone is not the only eternal.
Objection 2: Further, it is written "Depart, ye cursed into eternal [Douay: 'everlasting'] fire" ( Mat. 25:41 ). Therefore God is not the only eternal.
Objection 3: Further, every necessary thing is eternal. But there are many necessary things; as, for instance, all principles of demonstration and all demonstrative propositions. Therefore God is not the only eternal.
On the contrary, Jerome says (Ep. ad Damasum. xv) that "God is the only one who has no beginning." Now whatever has a beginning, is not eternal. Therefore God is the only one eternal.
I answer that, Eternity truly and properly so called is in God alone, because eternity follows on immutability; as appears from the first article. But God alone is altogether immutable, as was shown above (Q[9], A[1]). Accordingly, however, as some receive immutability from Him, they share in His eternity. Thus some receive immutability from God in the way of never ceasing to exist; in that sense it is said of the earth, "it standeth for ever" ( Eccles. 1:4 ). Again, some things are called eternal in Scripture because of the length of their duration, although they are in nature corruptible; thus ( Ps. 75:5 ) the hills are called "eternal" and we read "of the fruits of the eternal hills." ( Dt. 33:15 ). Some again, share more fully than others in the nature of eternity, inasmuch as they possess unchangeableness either in being or further still in operation; like the angels, and the blessed, who enjoy the Word, because "as regards that vision of the Word, no changing thoughts exist in the Saints," as Augustine says (De Trin. xv). Hence those who see God are said to have eternal life; according to that text, "This is eternal life, that they may know Thee the only true God," etc. ( Jn. 17:3 ).
Reply to Objection 1: There are said to be many eternities, accordingly as many share in eternity, by the contemplation of God.
Reply to Objection 2: The fire of hell is called eternal, only because it never ends. Still, there is change in the pains of the lost, according to the words "To extreme heat they will pass from snowy waters" ( Job 24:19 ). Hence in hell true eternity does not exist, but rather time; according to the text of the Psalm "Their time will be for ever" ( Ps. 80:16 ).
Reply to Objection 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.
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.
Objection 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.
Objection 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.