Summa summae S. Thomae sive compendium theologiae

St. Thomas, q. 10.

[Eternity is defined by Boethius, Consol. phil., III, 2: « The whole, simultaneous, and perfect possession of unending life. » This definition is commonly received.

It is explained¹. It is called possession, and not duration: not that eternity is not duration, as will be said below, but because duration, by force of the term, implies a certain distinction of parts, which must not be understood in the divine being. Boethius therefore said possession, speaking metaphorically, to designate the immutability and unfailingness of eternity; for that which is possessed is held firmly and quietly.

It is called possession of life², rather than of being: 1° because that which is truly eternal is not only a being, but a living being; 2° because living itself extends in a certain way to operation, whereas being does not; but eternity is the permanence of a thing invariable in being and in operating.

It is called of unending life³, to designate that eternity neither has nor can have a beginning and an end.

It is called possession⁴, whole and simultaneous⁵, to signify that eternity lacks division and succession according to before and after, such as is found in time, of whose nature it is to be successive, since it is the measure of motion. But eternity consists in a single now, or everlasting and indivisible instant, which is never past nor future, but always now.

It is called perfect⁶, to exclude the now of time, which, although it is whole and simultaneous, and has no parts, is nevertheless not something perfect in the nature of duration, since it vanishes immediately, nor is anything perfectly possessed in it.

The sense, therefore, of Boethius's definition is that eternity is the whole and simultaneous and unfailing duration of a living being, lacking succession, beginning, and end.

From this you will gather⁷, that eternity differs from aeviternity and time, not precisely because eternity lacks a beginning and an end, and aeviternity has a beginning but not an end, while time has a beginning and an end; for this difference is only accidental. For even if it were supposed that aeviternity had no beginning, and that time would have neither beginning nor end, they would nevertheless still be distinguished from eternity. Their true difference, therefore, lies in this: that aeviternity is the duration of a thing immutable as to substantial being, but mutable accidentally, for instance as regards place or operation, as in the angels; hence, on this score, it is not wholly simultaneous. And time is the duration of a thing variable as to being and operating; for it is the measure of motion according to before and after: hence in no respect is it wholly simultaneous, but flows through parts. But eternity, on the other hand, is the wholly simultaneous duration of a being invariable in being and in operating.

You will ask whether God, and He alone, is eternal.

I answer in the affirmative⁸.

Proof 1°. It is of faith, as defined in the Fourth Lateran Council: « We firmly believe and simply confess that there is only one true God, eternal, immense, etc. »

Proof 2°, from Scripture. Deuter., XXXII, 40: I live forever. Ps. IX, 8: The Lord endures forever. Ps. CI, 28: You are the very same, and your years do not fail. Dan., VI, 26: He is the living and eternal God forever. II Machab., I, 24 and 25: God the creator of all things..., alone excellent, alone just, alone omnipotent and eternal.

Proof 3°, from reason⁹. Eternity follows upon immutability, just as time follows upon motion. But God, and He alone, is essentially immutable. Therefore God, and He alone, is essentially eternal.

Nor is He only eternal, but He is really His own eternity¹⁰, just as He is His own goodness and His own wisdom; because He is His own being, which belongs to no creature. But eternity is nothing other than the duration of the divine being, or the divine being itself enduring. It is, however, virtually distinct from the divine being, as are the other attributes, because duration and being in creatures pertain to diverse genera. And although duration in creatures is not distinguished entitatively from the thing enduring — for it is the very thing enduring — it is nevertheless distinguished modally; for it is a mode of the thing: so that, although there cannot be duration without the existence of the thing, there can nevertheless be existence without duration properly so called, as if a thing should cease to be as soon as it began to be.

When, therefore, certain words of past, present, or future time are said of God, as in Apoc., I, 8: The Lord God, who is, and who was, and who is to come, these are not to be understood as though God were successively varied through present, past, and future, but because His eternity includes all the differences of times. Similarly, when successive operations of God are designated, the succession must not be taken on the side of the principle, but on the side of the effects.

Augustine illustrates this truth splendidly, Tract. 99 in Ioann., n. 5: « Concerning that which is everlasting, without beginning and without end, whatever word of any time is used — whether of the past, the present, or the future — it is not used falsely. For although that immutable and ineffable nature does not admit was and will be, but only is; for it truly is, because it cannot be changed, and therefore it was fitting for it alone to say: I am who am, and: You shall say to the children of Israel: He who is has sent me to you. Exod., III, 14: nevertheless, on account of the mutability of the times in which our mortality and our mutability are engaged, we say, not falsely, both was, and will be, and is. He was in past ages, He is in the present, He will be in the future. He was, because He was never absent; He will be, because He will never be absent; He is, because He always is. For He does not, as though He now were not, perish with things past; nor, as one who does not remain, does He slip away with things present; nor, as one who had not been, will He arise with things future. Accordingly, although human speech varies according to the passing of the times, concerning Him who through no times could fail, can fail, or will be able to fail, the words of any time whatsoever are truly spoken. »]