Cambridge, 1938–2020

D. H. Mellor

McTaggart was right that past, present and future are contradictory, and wrong that time needs them. Tensed facts do not exist. Tensed beliefs do, and we could not act without them.

The view

David Hugh Mellor spent most of his career at Cambridge. His book Real Time (1981), rewritten as Real Time II (1998), is the most influential defence of the B-theory, or tenseless theory, of time: the view that the only temporal facts are facts about which events are earlier or later than which, and by how much.

On this view there is no moving present. "Now" is like "here". Every moment is now at itself, as every place is here at itself, and neither picks out anything objectively special.

The argument

Tensed sentences have tenseless truth conditions. A tensed sentence can be true at one time and false at another, so its truth must depend on when it is said. Mellor's account: any particular saying, or "token", of "Waterloo is past" is true if and only if that saying is later than Waterloo. Nothing in that condition is tensed. The facts that make tensed talk true are B-series facts.

A saying of "e is past" is true just when it is later than e. after Mellor, Real Time II (1998)

McTaggart's contradiction is real. Mellor defends a version of McTaggart's argument: if events really had tensed properties, every event would have incompatible ones. Unlike McTaggart he takes this as a reason to reject tensed facts, not time.

Change is B-series change. Something changes when it has one property at one time and an incompatible one at a later time. A poker is hot at one time and cold at another. That is all change needs.

Tensed beliefs are indispensable. To catch a train, it is no use knowing that it leaves at 10.15; you must believe that it leaves now, or in five minutes. Tensed beliefs are what turn knowledge into timely action. That is why we have them, and why we cannot do without them, even though the facts that make them true are tenseless.

Time's direction comes from causation. In Real Time II Mellor argues that the order of earlier and later is fixed by the order of cause and effect: causes precede their effects because that is what "earlier" consists in.

Where he meets Deutsch

Of all the views on this site, Mellor's is closest to the spacetime picture in Deutsch's chapter. Both deny that time flows. Both say "now" is like "here": singled out from a point of view, but not objectively. Both treat change as the difference between how things are at one moment and how they are at another.

Both also explain our tensed outlook rather than dismissing it. For Mellor, tensed beliefs are what make timely action possible. For Deutsch, we experience differences between present perceptions and memories, and interpret them, wrongly, as something moving through time.

Where they part

Causation. Mellor builds time's direction out of causation within a single spacetime. Deutsch argues that this cannot work. In spacetime, exactly one thing happens, so claims about what would have happened otherwise have no clear meaning, and causation, which depends on them, has no place. Only the multiverse, where the variants really exist, makes sense of cause and effect.

One world or many. Mellor's B-series is a single ordering of events in one world. Deutsch's snapshots do not form one ordered series; other times are a special case of other universes, and the sequence of moments is only an approximation.

The open future. In Mellor's tenseless world, the future is fixed in the sense that its contents are there, just as the past's are. Deutsch says that in spacetime physics openness is an illusion, and that the multiverse restores it, relative to each observer.

See every view compared →

Further reading

• D. H. Mellor, Real Time (Cambridge, 1981).
• D. H. Mellor, Real Time II (London, 1998).
• Robin Le Poidevin and Murray MacBeath (eds), The Philosophy of Time (Oxford, 1993).
• Time, Stanford Encyclopedia of Philosophy, on the A- and B-theories.