Eternity

How does St. Thomas Aquinas understand eternity? Does it mean something more than just “forever”? Is it still related to time?

In the tenth question of the Summa, St. Thomas addresses The Eternity of God. He uses five articles to take us from the definition of eternity, to its application in God, to finally its relationship with time.

The definition of eternity

Not surprisingly, St. Thomas starts with a definition of eternity. He intends to use the interesting definition from Boethius, and then defends his choice of this definition. Although this definition is a bit long and complex, it pays off in the end, as a clear definition makes the answers to some complex questions my simpler.

In Book 5 of “The Consolation of Philosophy” Boethius defines eternity like this:

… eternity is at once the total and perfect possession of interminable life…

St. Thomas modifies the definition slightly from this translation, using this definition:

The simultaneously-whole and perfect possession of interminable life.

The change does not seem to be significant though. It may just be due to a difference in translation.

Important terms

To explain his definition, St. Thomas uses a few words which might seem to have odd meanings to us:

• Simple: Here simple does not mean unintelligent, but rather, it is the opposite of compound. St. Thomas spends question 3 discussing the simplicity of God. From that we can better understand what he means by “simple”. Something which is simple:

  1. Does not have distinct parts we can count
  2. Does not have matter and form
  3. Does not have subject and accident

  These attributes are a few among others listed in the article “Whether God is altogether simple?”. Simple represents some kind of wholeness and consistency. For St. Thomas, God is simple, almost everything else is not.

• Compound: Compound means the opposite of simple. Anything which has distinct parts is compound. So most things we experience with our senses are compound.

  I find the use of the words simple and compound in this way difficult to follow; in my mind simple tends to mean “easy to understand” and compound often means “difficult to understand”. St. Thomas, however, views simple in compound in the opposite way:

  we attain to the knowledge of simple things by way of compound things

  This is important to keep in mind as we go forward.

• Movement: We tend to think of movement as a change in position, like when we walk from one place to another. For St. Thomas, movement is more general, meaning any kind of change.

  a thing bereft of movement, which is always the same

  For example, arithmetic has no movement: the fact 1 + 1 = 2 will never change. If I apply arithmetic to something physical - say I have one cookie and another cookie, then I eat them both - now I have changed, and movement has occurred.

Two parts of the definition

With a better understanding of these words in mind, we can see now how St. Thomas addresses the two parts of this definition (although in the reverse order they appear).

• Time is the numbering of change (movement) with words like before and after.
• If something does not change (e.g. 1 + 1 = 2), then we don’t say is has any before or after.
• We say this thing which does not change is eternal.

So eternal things live in the opposite of time. Eternity is the way we express the immutability of things that do not change. These things which do not change do not start or terminate, so we call them interminable.

In addition, something which does not have a beginning and an end as no succession, meaning we cannot number its changes. For example, the life of of a person has succession: they are baby, then a child, then an adult. An arithmetic fact like 1 + 1 = 2 does not.

Finally, since 1 + 1 = 2 never gets more or less “arithmeticy” then we can say that it always a whole arithmetic fact. St. Thomas uses the work simultaneously to mean always.

So the two parts of the definition are then:

1. Something that does not have a beginning or an end is called interminable.
2. Something that has no succession is simultaneously-whole.

Since we use both of these concepts to describe eternity, we say that eternity is the simultaneously-whole and perfect possession of interminable life. I read this as “eternity is the name for existence without beginning or end where everything is as full and perfect as it can be.”

How does eternity differ from time?

It might be appealing to consider eternity to be time without beginning or end. But St. Thomas explains that this is not really a proper analogy. Indeed some believe that time will not end, so how can it differ from eternity? The definition above provides a succinct answer to this question:

eternity is the measure of a permanent being; while time is a measure of movement

In addition, we regularly speak about different parts of time, like the beginning and end of each day. Since eternity is simultaneously whole, it does not have different parts, and is therefore different from time.

How does eternity apply to God?

Recall from the definition above that St. Thomas uses the word “movement” in the same sense we use the word “change”. Recall that

• Time is the measure of movement (change)
• Eternity is the measure of immutability

God is immutable, therefore God is eternal.