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 Phys. 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.
Reply to Objection 1: Spiritual creatures as regards successive affections and intelligences are measured by time. Hence also Augustine says (Gen. ad lit. viii, 20,22,23) that to be moved through time, is to be moved by affections. But as regards their nature they are measured by aeviternity; whereas as regards the vision of glory, they have a share of eternity.
Reply to Objection 2: Aeviternity is simultaneously whole; yet it is not eternity, because "before" and "after" are compatible with it.
Reply to Objection 3: In the very being of an angel considered absolutely, there is no difference of past and future, but only as regards accidental change. Now to say that an angel was, or is, or will be, is to be taken in a different sense according to the acceptation of our intellect, which apprehends the angelic existence by comparison with different parts of time. But when we say that an angel is, or was, we suppose something, which being supposed, its opposite is not subject to the divine power. Whereas when we say he will be, we do not as yet suppose anything. Hence, since the existence and non-existence of an angel considered absolutely is subject to the divine power, God can make the existence of an angel not future; but He cannot cause him not to be while he is, or not to have been, after he has been.
Reply to Objection 4: The duration of aeviternity is infinite, forasmuch as it is not finished by time. Hence, there is no incongruity in saying that a creature is infinite, inasmuch as it is not ended by any other creature.
Whether there is only one aeviternity?
Objection 1: It seems that there is not only one aeviternity; for it is written in the apocryphal books of Esdras: "Majesty and power of ages are with Thee, O Lord."
Objection 2: Further, different genera have different measures. But some aeviternal things belong to the corporeal genus, as the heavenly bodies; and others are spiritual substances, as are the angels. Therefore there is not only one aeviternity.
Objection 3: Further, since aeviternity is a term of duration, where there is one aeviternity, there is also one duration. But not all aeviternal things have one duration, for some begin to exist after others; as appears in the case especially of human souls. Therefore there is not only one aeviternity.
Objection 4: Further, things not dependent on each other do not seem to have one measure of duration; for there appears to be one time for all temporal things; since the first movement, measured by time, is in some way the cause of all movement. But aeviternal things do not depend on each other, for one angel is not the cause of another angel. Therefore there is not only one aeviternity.
On the contrary, Aeviternity is a more simple thing than time, and is nearer to eternity. But time is one only. Therefore much more is aeviternity one only.
I answer that, A twofold opinion exists on this subject. Some say there is only one aeviternity; others that there are many aeviternities. Which of these is true, may be considered from the cause why time is one; for we can rise from corporeal things to the knowledge of spiritual things.
Now some say that there is only one time for temporal things, forasmuch as one number exists for all things numbered; as time is a number, according to the Philosopher (Phys. iv). This, however, is not a sufficient reason; because time is not a number abstracted from the thing numbered, but existing in the thing numbered; otherwise it would not be continuous; for ten ells of cloth are continuous not by reason of the number, but by reason of the thing numbered. Now number as it exists in the thing numbered, is not the same for all; but it is different for different things. Hence, others assert that the unity of eternity as the principle of all duration is the cause of the unity of time. Thus all durations are one in that view, in the light of their principle, but are many in the light of the diversity of things receiving duration from the influx of the first principle. On the other hand others assign primary matter as the cause why time is one; as it is the first subject of movement, the measure of which is time. Neither of these reasons, however, is sufficient; forasmuch as things which are one in principle, or in subject, especially if distant, are not one absolutely, but accidentally. Therefore the true reason why time is one, is to be found in the oneness of the first movement by which, since it is most simple, all other movements are measured. Therefore time is referred to that movement, not only as a measure is to the thing measured, but also as accident is to subject; and thus receives unity from it. Whereas to other movements it is compared only as the measure is to the thing measured. Hence it is not multiplied by their multitude, because by one separate measure many things can be measured.
This being established, we must observe that a twofold opinion existed concerning spiritual substances. Some said that all proceeded from God in a certain equality, as Origen said (Peri Archon. i); or at least many of them, as some others thought. Others said that all spiritual substances proceeded from God in a certain degree and order; and Dionysius (Coel. Hier. x) seems to have thought so, when he said that among spiritual substances there are the first, the middle and the last; even in one order of angels. Now according to the first opinion, it must be said that there are many aeviternities as there are many aeviternal things of first degree. But according to the second opinion, it would be necessary to say that there is one aeviternity only; because
