Two definitions that do not agree, and a committee deciding which one civil time follows.
Time
The order and passage of events - and the question of whether passing is a feature of the world or of the observer.
- Theme
- Cause, time and change
- Tradition
- Cross-tradition
- Term
- χρόνος · chronos
- Term fixed
- c. 397
In plain terms
Two claims about time are both very hard to give up and hard to hold together.
The first is that the present is special. Now is happening; the past is over; the future has not arrived. That is not a fact about my position - it seems to be a fact about the world.
The second comes from physics. Relativity has no universal present: whether two distant events are simultaneous depends on the observer's motion, and the equations treat time as a dimension with no preferred direction. On that picture the difference between past, present and future is, as Einstein wrote, a stubbornly persistent illusion.
One of those has to give, and neither side has persuaded the other. Meanwhile the practical business of measuring time has turned out to require decisions rather than discoveries.
As a philosopher would put it
The metaphysical division is between the A-series and B-series, from McTaggart: the A-series orders events as past, present and future, and the B-series as earlier and later. Presentism holds that only present things exist; the block universe or eternalism holds that all times are equally real and that passage is perspectival; the growing block holds that the past and present exist and the future does not.
Relativity presses hard on presentism, since simultaneity is frame-relative and a universal present has no invariant meaning.
Against this stands the phenomenological tradition. Augustine locates past and future in the soul's memory and expectation. Husserl's analysis of retention and protention describes the thickness of the present as experienced. Bergson's durée is lived time, continuous and heterogeneous, which he argues the spatialised time of physics distorts rather than measures - a claim his 1922 exchange with Einstein put on public record and lost.
Where you meet it
Atomic clocks keep time far more regularly than the earth does. The earth's rotation is irregular and slowing, so atomic time and solar time drift apart.
Since 1972 the answer has been the leap second: an extra second inserted into Coordinated Universal Time when the discrepancy approaches nine tenths of a second. Twenty-seven have been added, all positive.
They cause trouble. A minute containing sixty-one seconds breaks software that assumes it cannot, and outages at large service providers have been traced to them. In November 2022 the General Conference on Weights and Measures resolved to stop inserting them by 2035, letting the discrepancy accumulate instead.
So the world's timekeeping has two definitions - one from an atomic transition, one from the planet's rotation - which do not agree, and a committee has decided which one civil time will follow. Whatever time is metaphysically, the time everyone actually uses is a negotiated instrument.
What is actually disputed
Whether passage is real.
The A-theorist holds that the present is objectively distinguished and that the passage of time is a genuine feature of reality, which fits experience exactly and fits relativity badly.
The B-theorist holds that all times are equally real and that the sense of passage is an artefact of how a temporally extended being processes information, which fits the physics and leaves the phenomenology unexplained - and the explanation owed is substantial, since the difference between remembering a loss and anticipating one is not obviously perspectival.
McTaggart's original argument concluded that time is unreal, on the ground that the A-series is required for change and is contradictory, since every event must be past, present and future. Almost nobody accepts the conclusion and the argument has never been decisively refuted, which is an uncomfortable position for a subject to be in for over a century.
Commonly confused with
- clock time Clocks measure a quantity by convention, and the leap-second decision shows how much of it is settled by committee.
- Change c. 500 BC Change happens in time and time is not identical with it. Whether time could pass with nothing changing is a real question.
- the direction of time Why time has an arrow is a separate question, usually answered thermodynamically, and it does not settle whether passage is real.
Defined against
- Change Whether time could pass with nothing changing, and whether change could occur outside time, is the pair's standing question
Philosophers
- Augustine of Hippo Time located in memory, attention and expectation
- Aristotle Time as the number of motion with respect to before and after
- Immanuel Kant Time as a form of intuition rather than a feature of things
- Henri-Louis Bergson Duration as lived and continuous, against the spatialised picture
- Martin Heidegger Temporality as the meaning of existence rather than a container for it
Works
- Confessions The eleventh book, on time
- Metaphysics Time as the measure of motion
- Critique of Pure Reason Time as a form of sensibility
- Creative Evolution Duration against measured time
- Being and Time Temporality as constitutive of existence
Schools
- Augustinianism Where time is interior
- Peripatetic school (Aristotelianism) Where it is the measure of motion
- German Idealism Where it is a form of intuition
- Phenomenology Where lived time is described
- Process Philosophy Where becoming is fundamental
- Early Theravada Buddhism Where momentariness makes the present all there is
Related concepts
Change c. 500 BC · Space 1716 · Becoming c. 500 BC · Finitude 1927 · Infinity c. 570 BC
Augustine's remark that he knows what time is until asked to explain it is the most quoted line on the subject; the modern debate turns on whether the present is metaphysically privileged, which physics and phenomenology answer differently.