McTaggart's Argument for the Unreality of Time

Every modern debate about the nature of time traces back to a single short paper: J. M. E. McTaggart's "The Unreality of Time" (1908), expanded in The Nature of Existence (1927). McTaggart argued, astonishingly, that time is unreal — that nothing really is past, present, or future, and nothing really changes. Almost no one accepts the conclusion. But the argument's machinery — its distinction between two ways of ordering events in time — became the permanent vocabulary of the field, and the dilemma it poses still forces every theory of time to declare itself. To understand the A-theory and the B-theory, presentism and eternalism, and the debate over passage, one must start here.

The A-series, the B-series, and the C-series

McTaggart observed that events in time can be arranged in two fundamentally different ways.

• The A-series orders events by their tensed position relative to the present: an event is future, then present, then past, receding ever further into pastness. These are monadic, one-place properties — being past simpliciter — and they change: the same event that is now present was future and will be past. The A-series is the series "running from the far past through the near past to the present, and then from the present through the near future to the far future."
• The B-series orders events by tenseless relations of earlier than and later than. These are two-place relations, and they are permanent: if the death of Queen Anne is earlier than the coronation of Elizabeth II, it always was and always will be earlier; that relation never changes.

He added a third, the C-series: the bare ordering of events in a sequence, with no direction and no time — like beads on a string that fix an order (this bead between those two) but not which end is "first." The C-series has order but not change or direction.

The argument in two steps

McTaggart's argument that time is unreal has a positive and a negative half.

Step 1: Time essentially involves the A-series. Time, McTaggart insists, essentially involves change. But where is the change? Consider any event — the death of Queen Anne. Its B-series relations never alter: it is eternally later than the Great Fire and earlier than the French Revolution. Its intrinsic character never alters. The only thing that changes about it is its A-series position: it was future, became present, and is now ever more past. So change is possible only through the A-series; the B-series alone gives a static ordering (in effect, only a C-series with a direction imposed). Hence without the A-series there is no change, and without change no time. The A-series is essential to time.

Step 2: The A-series is contradictory. But the A-series, McTaggart argues, cannot be real, because the A-properties are mutually incompatible yet must all be possessed by every event. Past, present, and future are exclusive: no event can be all three at once. Yet every event is all three — the death of Queen Anne is past now, but it was present, and was (earlier still) future. So each event has incompatible properties.

The natural reply: it does not have them at once; it is future, then present, then past — at different times. McTaggart's rejoinder is that this reply generates a vicious regress. To say the event "is present, was future, and will be past" is to invoke a second A-series — the tenses of the tenses — and to specify those we need moments (past moments at which it is present, etc.). But those second-order tenses face exactly the same problem: each moment-of-time is itself past, present, and future, and so on without end. At every level the incompatibility recurs and the fix presupposes what it was meant to explain. The A-series can never be coherently constituted.

Conclusion. Time requires the A-series (Step 1); the A-series is self-contradictory (Step 2); therefore time is unreal. What is real is at most the directionless C-series, an ordering our minds mistakenly experience as a flowing time.

The structure of the dilemma

The lasting power of the paper is that it presents later theorists with a forced choice, since almost everyone rejects the conclusion:

This is exactly the fork developed on the A-theory / B-theory page. The A-theorist typically holds that the "contradiction" is an artifact of trying to state tensed facts in a tenseless metalanguage: at present, the event is present and not past, full stop — there is no moment at which it has incompatible tenses, so no contradiction. The B-theorist accepts Step 2 but rejects Step 1, arguing (with Russell) that change can be analysed tenselessly — a poker is hot at $t_1$ and cold at $t_2$, and that is change, requiring no A-series at all.

Why it still matters

McTaggart's own idealist conclusion (that reality is a timeless C-series of perceptions) died with his system. What survived is threefold:

1. The vocabulary. "A-series" and "B-series," "A-theory" and "B-theory," are now the standard names for the tensed/tenseless divide — the single most useful distinction in the philosophy of time.
2. The challenge to the A-theorist. The regress in Step 2 is a genuine and lasting problem: any theory that posits objective, changing tense owes an account of how the tenses relate without vicious regress or hidden circularity. Modern A-theories (presentism, the moving spotlight) are in part responses to McTaggart.
3. The challenge to the B-theorist. Step 1 puts the burden on the B-theorist to show that a tenseless world genuinely contains change and time rather than a mere frozen ordering — the "loss of passage" worry that recurs in the passage and block universe debates.

Where this sits

McTaggart's argument is the historical and conceptual gateway to the temporal question — the second of the section's three master questions. It manufactures the A/B distinction that the A-theory / B-theory page develops, sets the agenda for presentism and eternalism (which are ways of being an A- or B-theorist about ontology), and frames the passage debate over whether time really flows. The next page takes up the fork McTaggart forced: the tensed A-theory against the tenseless B-theory.