1. Having established that God alone is truly eternal, and given a basic division of the degrees of participation in God's eternity, St. Thomas next asks how Eternity differs from Time. This will be essential in accounting for the quasi-eternity of the angels later on in the question.
2. He gives three objections: First, that two measures of duration cannot be simultaneous without one being part of the other. Since eternity and time are simultaneous, and eternity cannot be part of time, time must be part of eternity.
3. Second, that since eternity is simultaneous and permanent, and the "now" is precisely what remains perpetual throughout time, eternity must be identical with the "now" of time. (Notice that this objection completely inverts the first objection. Here Eternity is the minutest part of time, there time was a part of eternity.)
4. Third, that Aristotle says that the measure of the first being is the measure of every other being. Well as regards temporality, eternity is the measure of God. But as regards temporality, time is the measure of everything else. So time and eternity must be the same, or time must at least be part of eternity.
5. He cites no authority in his Sed Contra, but gives a brief argument: Eternity is simultaneously whole, but time includes "before" and "after". Therefore they are distinct.
6. In the Corpus he explains. Time and eternity differ, not simply because time has a beginning and an end, where eternity has neither, since we could conceive of time being beginningless and unending (or at least many philosophers have held that idea). Rather, they differ essentially because eternity is simultaneously whole, where time involves succession. He argues again on the basis of what is measured by each thing: what is measured by time always has a beginning and an end, since there cannot be an infinite duration in time. But what is measured by eternity has no beginning or end. And he gives a third argument based on the way each measures its object: time is in potency to division (by beginning and end and quantity of motion), where eternity is not in potency to any division, because it is perfect and simultaneously whole.
7. He draws on the corpus to answer the first objection: time and eternity are different kinds of measures (one of the quantity of motion, the other of the permanence of a thing), and therefore they can be simultaneous without either being part of the other.
8. To the second he says that the "now" which is present throughout time, differs from moment to moment according to what it contains, because the new is always the now of actual, mobile things. But eternity does not change, either in itself or in what is subject to it, or in any of its aspects.
9. Finally, he answers the third objection by saying that the more mutable a thing is, the more it recedes from eternity and is measured by time. And, the more permanent a thing is, the more it recedes from time and is measured by eternity.
OUTLINE OF ARTICLE
- Two measures of duration cannot be simultaneous unless one is part of the other.
- The “now” is eternity.
- The measure of the first being is the measure of every other being.
- Time and eternity differ, but not because time has a beginning and end (since it could conceivably not).
- They differ because eternity is simultaneously whole, but time involves succession.
- They differ by what they measure, and how they measure it.
- They are different kinds of measures.
- The “now” changes based on what it is subject to from one moment to the next.
- The more a thing is mutable, the more it is measured by time. The more it is immutable, the more it is measured by eternity.