Time

Key terms

What time is

Time and eternity

Feeling and use

Measure of motion

What do we count when we count time? Time is often taken to be a measure of motion: we reckon it by what changes, by a before and an after. These readings ask whether time is anything apart from the things that move.

3 readings

In Book IV, chapter 11, of the Physics, Aristotle completes his inquiry into time, which he has treated through chapters 10 to 14, and reaches the definition: “number of motion in respect of ‘before’ and ‘after’”. He speaks of the “now”, of “movement” and of “number”. The definition was the starting point for later discussion of time, scholastic and modern. It sits under “Measure of motion” as that definition.

In Book I of On the Nature of Things, Lucretius, expounding the atomism of Epicurus in Latin verse, distinguishes what exists “of itself” from the “accidents” of slavery, poverty, wealth, war and concord. Time is placed among the accidents, as something the “sense” reads out of things. The poem is the fullest surviving statement of Epicurean physics. It sits under “Measure of motion” as a statement that time is not felt apart from “motion and repose”.

In the Summa Theologica, First Part, question 10, article 1, Aquinas asks whether “eternity” is rightly defined by Boethius, and in the “I answer that” explains the idea by way of its contrary, time. He takes time to be “the numbering of movement by ‘before’ and ‘after’”, which is the Aristotelian definition. The article is the usual scholastic reference for the relation of the two. It sits under “Measure of motion” as the Aristotelian definition in the Summa.