Is Time Real?

J. M. E. McTaggart famously argued that time is not real. By this, he meant that there are no things to which either of two sets of temporal concepts apply: "A-concepts", viz. past, present, future, two years past, two years in the future, etc.; and "B-concepts", earlier than, later than, and simultaneous with.

McTaggart's argument consists of two-parts. The first part contends that the "tenseless theory of time," according to which the A-concepts are reducible to the B-concepts (via token-reflexive definitions), or perhaps completely eliminable (i.e. are never applicable), is wrong; or as McTaggart puts it, "there can be no A-series [things to which the A-concepts apply] without a B-series [things to which B-concepts apply]." The second part of the argument purports to show that the "tensed theory of time", according to which the B-concepts are not reducible to the A-concepts, is contradictory. If neither theory of time is correct, then, it must be because there is no such thing as time, i.e. no things to which the A or B concepts apply.

McTaggart's argument against the tenseless view of time is that on the tenseless view of time, represented by Russell, we cannot make sense of the possibility of change; and if there is no change, then there is no time.

McTaggart argues as follows. Take some event, e.g. the death of Queen Anne. "That it is a death, that it is the death of Anne Stuart, that it has such causes, that it has such effects - every characteristic of this sort never changes." (26) The only thing about the death of Queen Anne that changes over time is whether it is future, present, or past, i.e. which of the A-concepts apply to it. And as it is with the death of Queen Anne, so it is with all events. Thus, if there is no A-series, there is no change, and hence no time.

The response by Russell, a proponent of the tenseless view of time, is that McTaggart is looking in the wrong place for change. Change is not present in events (at least not in momentary events), but in persisting objects. To say that a something has changed is to just to say that a persisting thing has some property at one time, and fails to have that property at another time, or in Russell's words, "Change is the difference, in respect of truth or falsehood, between a proposition concerning an entity and the time T1, and a proposition concerning the same entity and the time T2, provided that these propositions differ only by the fact that T1 occurs in the one where T2; occurs in the other." (Quoted by McTaggart, 27)

McTaggart states that he agrees that this would suffice for change, but thinks that this response is question-begging, for it assumes the existence of times; and according to McTaggart, if there is no irreducible A-series, there are no times. So rather than say, e.g., that this poker is hot at one time and is not hot at another time, let us say that the poker is hot on Monday, and is not hot on Tuesday, remaining neutral on whether Monday and Tuesday are indeed times. Does this suffice for there to be change?

McTaggart claims that it does not, for if the poker is hot on Monday, it is always hot on Monday, and if it fails to be hot on Tuesday, it always fails to be hot on Tuesday. Neither of these relations of the poker to Monday and Tuesday change. The only thing that could change, claims McTaggart, is whether the poker is hot in the future, present, or past, i.e. whether Monday and Tuesday themselves are future, present, or past. And to account for change, the futurity, presentness, and pastness of events cannot merely be the sort of futurity, pastness and presentness given by a token-indexical analysis of these concepts, according to which "past" means "earlier than this utterance," "present" means "simultaneous with this utterance," and "future" means "later than this utterance". For if this were all that were meant, a given event, such as the poker's becoming hot, would eternally be future on Sunday, present on Monday, and past on Tuesday, and there would be no change.

To reinforce this, McTaggart asks us to make a comparison with having certain properties in relation to another sort of series, a spatial one, viz. the series of latitude lines. At 50 degrees latitude, the Greenwich meridian is in England, and at 0 degrees; latitude, it is not. But, claims McTaggart, we do not wish to say that the Greenwich meridian undergoes any change in virtue of its differing relation to points in a spatial series, for it is always the case that (at least since there has been an England) the Greenwich meridian is in England at 50 degrees latitude, and not in England at 0 degrees latitude.

Since the B-series by itself cannot account for change, there is change, and hence time, only if there is an irreducible A-series. But McTaggart claims that any theory that makes use of irreducible A-concepts is contradictory. For the properties (or relations, if such they be) of pastness, presentness, and futurity are (a) incompatible, in that it is conceptually impossible for a thing to have more than one; but (b) if a thing has one of these properties, it must have more than one of them: the death of Queen Anne was future, then was present, and now is past.

McTaggart anticipates the reply: yes, these properties are incompatible, and all events have all three; but nothing has more than one of these properties at any given time. An event that is present was future, and will be past.

McTaggart answers this reply first with an analysis of "is", "was", and "will be": to say that X was Y, according to McTaggart, is to say that X is Y at a past moment; and to say that X will be Y is to say that X is Y at a future moment. But what of these moments that are past, present, or future? These moments must too have the incompatible properties of pastness, presentness, and futurity; and hence the contradiction has not been escaped.

If a similar reply is given for these moments, McTaggart asks again about the new moments relative to which these moments are past, present, or future: and claims that the contradiction has not yet been escaped. "And so on infinitely", McTaggart writes. "Such an infinity is vicious. …The first set of terms never escapes contradiction at all."

Does time flow?

Even if McTaggart is wrong, and the tenseless view of time can make sense of change by locating it in persisting objects and not momentary events, the tenseless view of time still faces a puzzle about the passage, or the flow, of time. It is a commonplace that time passes, or flows. Admittedly this is metaphorical, but what literal truth lies behind the metaphor: or is the metaphor entirely misleading when it comes to metaphysics?

The puzzle is this. A river flows or passes in virtue of the fact that its constituent drops of water become successively closer and closer to, and then further and further away from, some spatial point regarded as fixed; i.e. at one point in time, t1, any given constituent drop of the river stands at a certain distance from the fixed spatial point, and at a successive time t2, it is closer to or further away from that point. How is it then that time flows or passes?

The advocate of the tensed view of time has an answer to this question. The constituent times that are future are becoming closer and closer to the NOW, and those that are future are receding from it.

It's not clear that the advocate of the tensed view of time is required to see the pastness, presentness, or futurity of an event or time as a literally relational property which depends on a time or event's relationship with this "NOW". This might too be taken as a metaphor, for the fact that futurity, an intrinsic property of certain events and times that comes in degrees, is gradually lost, until the object is present, at which time the event or time begins to gain intrinsic pastness.

Or an advocate of the tensed view might try to explain the metaphor without an appeal to an ontology of past and future events or times. This is the position of Arthur Prior. Prior views the tenses as unanalyzed one-place sentential operators: "I fell out of a punt" is analyzed as "It was the case that I am falling out of a punt"; I will have received my doctorate" as "It will be the case that it was the case that I am receiving my doctorate." Prior also requires more specific tense-operators: "It was the case three years ago", "It will be the case six weeks hence", etc.

To say that something has changed is to say this, according to Prior. Something that was the case is no longer the case, i.e. for some sentence S, to say "It was the case that S, and it is not now the case that S. Now the sentence S itself may have some tense operators on the front of it, as these operators are iterable. It was the case two months ago that was the case three weeks ago that I am getting married, and it is not now the case that three weeks ago I am getting married. It is this systematic change of the truth value of tensed sentences that is the literal truth behind the metaphor of time's passage or flow, according to Prior.

The advocate of the tenseless view of time has no such easy explanation of the metaphor of time's passage or flow. The advocate of the tenseless view of time analyzes such expressions as "now", "is past", "is future", as well as Prior's sentential operators "It was the case that" and "it will be the case that", in terms of McTaggart's B-concepts, by construing them as token-indexicals. "E is happening now" just means "E is simultaneous with this utterance"; "It was the case that P" just means "Earlier than this utterance, P". But these B-concepts attributed to events, times, or sentences, are eternally applicable. If an utterance of "The Civil War is past" at just means "The Civil War occurred prior to this utterance", that utterance is, if true, eternally true, and if false, eternally false. What changes, on the tenseless view of time, is not the pastness, presentness, and futurity of events, times, or sentences, for there is no property, intrinsic or relational, unambiguously designated by our "A-words". What changes (in David Kaplan's terminology) is the one aspect of the meaning of the A-words, the content of sentences containing them. (Although the character of the sentences remains constant.)


References

McTaggart, J. M. E. "The Unreality of Time", in Robin Le Poidevin and Murray MacBeath, eds., The Philosophy of Time. Oxford, 1993.

Prior, Arthur. "Changes in Events and Changes in Things," in Le Poidevin and MacBeath, op. cit.

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