Reply Obj. 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 Obj. 2: Aeviternity is simultaneously whole; yet it is not eternity, because "before" and "after" are compatible with it.
Reply Obj. 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 Obj. 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. _______________________
SIXTH ARTICLE [I. Q. 10, Art. 6]
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."
Obj. 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.
Obj. 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.
Obj. 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.