QuestionsDoes time really exist?Time is unreal: the series of past, present and future contradicts itself
Does time really exist?Passage is an illusion

Time is unreal: the series of past, present and future contradicts itself

The A series and the B series; the unreality of time

J. M. E. McTaggart 1866 · 1925He argues that time is not real: past, present and future contradict each other, and without them there is no change.
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What it claims

The A series cannot be true of reality. Since time requires the A series, time is not real: whenever we judge that something exists in time, we are in error.

Why

An event would be past, present and future at once, which is contradictory, and explaining it by time is circular.

The same idea through history
Parménide475 BCParmenides holds that what is neither comes to be nor passes away: change is only an appearance. McTaggart reaches a similar conclusion by another road, a logical proof.
Immanuel Kant1781Kant denies that time is a property of things in themselves. McTaggart lists Kant among the philosophers who held time unreal, but bases his thesis on a different argument.
J. M. E. McTaggart1908McTaggart gives the proof: time requires the A series, and the A series is contradictory. It is taken up again in 1927 in The Nature of Existence, published after his death.
In short

"Time is unreal: the series of past, present and future contradicts itself" is an argument by J. M. E. McTaggart ('The Unreality of Time', Mind, 1908, 1908) on the question "Does time really exist?" (answer: passage is an illusion). Its claim: The A series cannot be true of reality. Since time requires the A series, time is not real: whenever we judge that something exists in time, we are in error. According to AskPhilosophy's logic check (Z3 solver), the conclusion does follow from its 5 premises. AskPhilosophy presents 3 objections, 1 of them with a documented reply, and the original text behind each premise, checked word for word.

'The Unreality of Time', Mind, 1908
Valid

Everyone feels that time passes: what is future becomes present, then past. McTaggart argues that this idea, taken seriously, is contradictory. An event cannot be past, present and future at once, and yet it is all three in turn. If we answer that it is so 'at different times', we already need time to explain time. So time is not real. Written in 1908, this argument has remained one of the most discussed in philosophy: some accept the A series and reject the argument, others accept the argument and keep only the order 'earlier/later'.

P1Moments of time are ordered in two ways. The B series puts them in 'earlier' and 'later': these relations are permanent. The A series puts them in past, present and future: these determinations change all the time (what is future becomes present, then past).
P2There is no time without change, and no change without the A series. In a B series alone, an event never begins or ceases to be that event. What changes is only its position as future, present, past.
P3The A series is contradictory. Past, present and future are incompatible determinations, and yet every event has them all: if it is past, it has been present and future.
P4The answer 'it is present, will be past, has been future' does not remove the contradiction. It presupposes time to explain how moments are past, present and future, whereas time presupposes the A series: a vicious circle.
P5An idea cannot be true of reality if its application to reality contains a contradiction that cannot be removed. It may be unexplainable, but not contradictory.
So the A series cannot be true of reality. Since time requires the A series, time is not real: whenever we judge that something exists in time, we are in error.

click a premise to reject it

If you accept every premise, logic forces you to accept the conclusion. So the debate is about the premises.
Checked by a logic solver: the premises cannot all be true while the conclusion is false.
Without the implicit premise: Without P5, the computer finds a case where the A series is contradictory with no way out and yet true of reality: for example if reality could tolerate certain apparent contradictions. His opponents therefore rarely dispute P5: hardly anyone accepts a contradictory reality.
Valid as it stands: McTaggart wrote his premises himself, there is no hidden premise. P2 links time to the A series, P3 and P4 say it is contradictory with no way out, P5 says a contradictory idea is not true of the real. Critics therefore do not attack the logic but the premises: P2 (Russell), P3 and P4 (Prior, Broad).
Analogy. Imagine a sign saying: 'This door is open, shut and half open.' You would answer: 'at different times.' McTaggart replies that this 'time' is already time: one cannot explain the passage of time by saying that there is time.

Objections

3

Each objection is a conversation: click to see who replies and where the debate stands.

Bertrand Russell 1903 · attacks premise 2

The B series is enough for change. To change is only for a thing to have a property at one time and not at another: change is the difference in truth between two propositions about the same thing, one about a time T, the other about another time T'. No need for 'past, present, future'.

no reply
We have not yet found a direct reply by McTaggart in the texts.
The debate goes on (our summary) McTaggart does not cite Russell. In the article (§ 11-20) he examines what could change in a B series alone (an event ceasing to be, an event becoming another, a moment of time) and concludes that none of these changes is possible, since the 'earlier/later' relations are permanent. He does not discuss Russell's definition as such.
Where the debate stands (our summary)Our summary: Russell's definition has become the standard definition of change among those who reject the A series. McTaggart would say it is not real change, since nothing changes in it: everything stays fixed. Core disagreement about what 'to change' means.
Arthur Prior 1959 · attacks premise 3

'Tensed' facts cannot be reduced to 'earlier/later' relations. When we say 'Thank goodness that's over', we are relieved that the pain is over now, not that it precedes this utterance. Past, present and future are therefore real and basic. With tense operators ('it was the case that', 'it will be the case that'), one can say that an event is present, was future and will be past, without speaking of moments at which it would be present or past: no circle.

McTaggart replies
see the argument
J. M. E. McTaggart 1908 · McTaggart's anticipated reply
McTaggart foresees the reply that time is ultimate, hence unexplainable without itself. He answers that an idea may be unexplainable and yet true of reality, but not if its application contains a contradiction: it is for this, and not because it is unexplainable, that he rejects time.
The debate goes on (our summary) This reply does not address tense operators: Prior's tense logic dates from 1957-1967, long after McTaggart. The question remains whether 'it will be present, it has been future' can be said with operators without quantifying over moments.
M
Michael Dummett defender of the argument · 1960
Dummett defends the validity of McTaggart's proof against the A series, in a paper devoted to that subject.
Where the debate stands (our summary)Our summary: supporters of the A series (Prior) and of the B series agree on one point: if the A series contains a contradiction, time is unreal. They part over the contradiction itself. An open point: no widely accepted answer.
C. D. Broad 1938 · attacks premise 3

Broad rejects McTaggart's diagnosis. The contradiction comes from the way McTaggart describes the A series, as 'characteristics' that every event would bear all at once. For Broad, becoming is an ultimate fact: what happens comes into existence, which is the passing of time itself. Broad draws from it a picture in which the past keeps growing and the future does not yet exist.

no reply
No reply possible: objection raised in 1938, after the author's death (1925).
Where the debate stands (our summary)Our summary: McTaggart died in 1925, before Broad's book (1938), which is an examination of his philosophy. The disagreement is about what becoming is: a sequence of characteristics borne by existing events (McTaggart) or the very coming into existence of new events (Broad). An open point.