Cambridge, 1866–1925

J. M. E. McTaggart

There are two ways of ordering events in time: as past, present and future, and as earlier and later. Time needs the first, and the first is contradictory. So, McTaggart concluded, time is unreal.

A painting of three heads, an old man, a man in his prime and a youth, above the heads of a wolf, a lion and a dog, with a Latin inscription — Titian, *An Allegory of Prudence*, mid-16th century. National Gallery, London. Past, present and future as three ages of a man. The inscription reads, in our translation: "From the past, the present acts wisely, lest it spoil the future."

The view

John McTaggart Ellis McTaggart spent his career at Trinity College, Cambridge, and was a British idealist: he held that reality is ultimately spiritual, a community of minds. His argument against time first appeared in the journal Mind in 1908 as "The Unreality of Time", and again in the second volume of The Nature of Existence, published after his death.

The argument is now read far more widely than the system it served. Its lasting gift is a vocabulary. McTaggart called the ordering of positions as past, present and future the A-series, and the ordering by earlier than and later than the B-series. Almost every later debate about time, including the ones on the next two pages, is conducted in these terms.

The argument

Time needs change. A world in which nothing changed would not be temporal at all.

The B-series alone has no change. If one event is earlier than another, it always is. Facts of that kind never alter. The only way an event can change, McTaggart said, is in its A-characteristics: his example was the death of Queen Anne, which was once future, became present, and is now past, and in no other way changes at all.

Without change there could be no time at all. after McTaggart, "The Unreality of Time" (1908)

So time needs the A-series. Without a moving present, the B-series is just an order, which McTaggart called the C-series. It becomes temporal only when the A-series is added.

But the A-series is contradictory. Past, present and future are incompatible: nothing can be both. Yet every event has all three. The obvious reply is that it has them at different times: it was future, is present, will be past. But those tensed words are themselves A-series terms. Saying "was future" means it is future at some past moment, and that moment in turn has all three properties. Every attempt at a fix rebuilds the problem one level up. The regress is vicious.

So time is unreal.

Few people accept the conclusion, but the two halves of the argument split later philosophers into camps. A-theorists, like Arthur Prior, reject the second half: the A-series is not contradictory. B-theorists, like D. H. Mellor, reject the first: time does not need the A-series, and change in the B-series is change enough.

The A-series: as the present moves, each event is future, then present, then past. For McTaggart, this is the only real change there is.

Where he meets Deutsch

The core of Deutsch's chapter runs closely parallel to McTaggart. Deutsch takes the common-sense picture, a line of moments with a moving "now", and argues that it does not make sense even in its own terms. If the present really moved from one moment to another, it would have to move with respect to a second, exterior time, which would need its own moving present, and so on without end. That is McTaggart's regress, arrived at from a different direction.

Deutsch also shows what is left once the moving present is removed. His figure 11.3 puts a "now" on every moment, at which point the labels single nothing out and can be dropped. What remains is an ordered series of moments: in McTaggart's language, a B-series without an A-series.

Where they part

Is the B-series enough? This is the decisive difference. McTaggart held that without a moving present there is no change, and so no time. Deutsch holds that change just is the difference between one snapshot and another. The rotating arrow points down in one and up in another; nothing more is needed.

The conclusion. McTaggart concludes that time is unreal and that reality is timeless spirit. Deutsch concludes only that the flow of time is unreal. Time itself, as a structure of snapshots related by law, is as real as anything.

Method. McTaggart works by pure metaphysical argument. Deutsch's case starts from a logical point but is completed by physics: relativity removes any objective "now", and quantum theory replaces the sequence of moments with something richer.

Ordering. McTaggart's C-series is an order without any direction. For Deutsch, the order of snapshots comes from the laws of physics, and the direction we feel from the way the variety of snapshots grows, the second law of thermodynamics in multiverse terms.

McTaggart and Deutsch side by side
	McTaggart	Deutsch
Does time flow?	Time would need flow, and flow is contradictory.	No. The idea is incoherent.
Is time real?	No.	Yes, as relations between snapshots.
What is change?	Only A-series change: future to present to past.	Differences between snapshots.
The key regress	Tensed fixes for the A-series repeat the contradiction.	A moving now needs an exterior time, without end.

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J. M. E. McTaggart

The view

The argument

Where he meets Deutsch

Where they part

Further reading