The Unreality of Time

"The Unreality of Time" is the best-known philosophical work of the Cambridge idealist J. M. E. McTaggart. In the paper, first published in 1908 in Mind 17: 457-73, McTaggart argues that time is unreal because our descriptions of time are either contradictory, circular, or insufficient. To frame his argument, McTaggart identifies two descriptions of time, which he calls the A-series and the B-series. The A-series identifies positions in time as past, present, or future; the B-series, as earlier than or later than some time position. Attacking the A-series, McTaggart argues that any event in the A-series is past, present, and future, which is contradictory in that each of those properties excludes the other two. He further urges that describing an event as past, present or future at different times is circular because we would need to describe those "different times" again by past, present, or future, and then again describe that description by past, present, or future, and so on. Attacking the B-series, McTaggart argues that time involves change, but because earlier-later relationships never change (e.g. the year 2010 is always later than 2000), the B-series must be an inadequate account of time.

The A-series
"...the series of positions running from the far past through the near past to the present, and then from the present to the near future and the far future..."

McTaggart says, "the distinctions of past, present, and future are essential to time and... if the distinctions are never true of reality, then no reality is in time." He considers the A-series to be temporal, a true time series because it embodies these distinctions and embodies change.

The B-series
"The series of positions which runs from earlier to later..."

The B-series is temporal in that it embodies a direction of change. However, McTaggart argues that the B-series on its own does not embody change itself.

The C-series
"...this other series — let us call it the C-series — is not temporal, for it involves no change, but only an order. Events have an order. They are, let us say, in the order M, N, O, P. And they are therefore not in the order M, O, N, P, or O, N, M, P, or in any other possible order. But that they have this order no more implies that there is any change than the order of the letters of the alphabet..."

According to McTaggart the C-series is not temporal because it is fixed forever. He also says that adding "change" to the C-series is not sufficient to get the B-series, because this would not determine the direction of time:

"...the C series, while it determines the order, does not determine the direction. If the C series runs M, N, O, P, then the B series from earlier to later cannot run M, O, N, P, or M, P, O, N, or in any way but two. But it can run either M, N, O, P (so that M is earliest and P latest) or else P, O, N, M (so that P is earliest and M latest). And there is nothing either in the C series or in the fact of change to determine which it will be...a person who contemplates a time-order may contemplate it in either direction...But in dealing with the time series we have not to do merely with a change in an external contemplation of it, but with a change that belongs to the series itself. And this change has a direction of its own...Therefore, besides the C series and the fact of change there must be given—in order to get time—the fact that the change is in one direction and not in the other. We can now see that the A series, together with the C series, is sufficient to give us time. For in order to get change, and change in a given direction, it is sufficient that one position in the C series should be Present, to the exclusion of all others, and that this characteristic of presentness should pass along the series in such a way that all positions on the one side of the Present have been present, and all positions on the other side of it will be present. That which has been present is Past, that which will be present is Future."

The general structure of the argument
McTaggart's argument for the unreality of time has two parts. In the first part, he argues that the B-series alone is insufficient for time to exist. In doing so, he also argues that the A-series is essential to time. Time demands change, and both the B- and C-series without the A-series do not involve change. Therefore, time must be described using the A-series.

In the second part, he argues for the conclusion that the A-series is incoherent because it leads to contradiction. Specifically, he argues that since every event that occurs will at one time be the future, at another time be the present, and at a third time (and forever henceforth) be past, every event exemplifies or instantiates every temporal property: futurity, presentness, and pastness.

Since these properties are mutually exclusive (they cannot be co-instantiated), the A-series conception of time generates an absurdity, a contradiction. If both parts of his argument are sound, then time must just be an illusion; it has no genuine ontological status.

The idea of change
McTaggart has defined two fixed series (the B- and C-series) and one series that is continuously created (the A-series). This is pivotal to his argument about the way things change. In the B- and C-series, things have fixed positions and fixed extents, so they cannot change. They are defined as static from the outset.

Of events in the B-series, McTaggart says, "No event can cease to be, or begin to be, itself, since it never ceases to have a place as itself in the B-series. Thus one event cannot change into another." and "As the B-series indicates permanent relations, no moment could ever cease to be, nor could it become another moment."

Given that the C-series is, like the B-series, a set of events cast in the same sequence forever, it is also unchanging, according to McTaggart. He says of events in the C-series, "...that they have this order no more implies that there is any change than the order of the letters of the alphabet..."

McTaggart argues that what we consider to be change is actually the inclusion of an event in the A-series: "But in one respect it does change. It began by being a future event. It became every moment an event in the nearer future. At last it was present.  Then it became past, and will always remain so, though every moment it becomes further and further past." He then asks whether such a change can really occur.

However, there have been attempts to account for the idea of change from some proponents of the B-series. Though, they reject tense overall, they disagree that time must also be so abandoned.

The nature of change
McTaggart asks if the change that occurs to an event in the A-series is a quality of the event or a relation between events. He considers that there is one relation that deserves consideration: "a past event changes only in one respect — that every moment it is further from the present than it was before"

The relative position of an event in the A-series might be considered as an indication of change. McTaggart then argues that this relationship shows that the A-series itself cannot exist.

The basic argument against the A-series notes that if events change by a relation in which they get farther from the present in the A-series, then one term of the relation would be in the C-series and the other term would be the present moment of the A-series. This means that: "The relations which form the A-series then must be relations of events and moments to something not itself in the time-series."

This concept then leads to other arguments against the A-series. In the first of these, it is pointed out that the terms future, past, and present are incompatible, yet each event has all three of these relations. McTaggart notes that this might be avoided by describing an event as has been future, is present and will be past. He believes this involves a vicious circle, because it assumes time to explain time, i.e. assumes another A-series in the future or past.

In the second argument, related to the first, it is pointed out that if each event has been future, is present, and will be past, then when one considers an A-series, there is yet another A-series where an event is present in the future, and so on ad infinitum. McTaggart calls this a vicious infinite series and argues, therefore, that the A-series is untenable.

It may be added that McTaggart's argument against the A-series rests on the assumption of two premises:

1.All events have the properties of past, present and future, at the same time.

2.That these A-properties are incompatible (or mutually-exclusive) with one another.

A person may object to the first premise, accusing McTaggart of assuming that all events have these properties at the same time. It is in assuming that all events start out with a contradiction that requires tensing that creates the regress, but once we reject this, the contradiction does not even take off. An event is said to be past, but is not also present nor future, and as well, an event is said to be present, but not past and future.

He concludes these arguments by stating that "Our ground for rejecting time, it may be said, is that time cannot be explained without assuming time."

Influence of "The Unreality of Time"
McTaggart's paper led to a number of productive areas in the philosophy of time. He laid the foundations for both the tensed and tenseless theories of time. He dismisses a relativistic approach but notes how it would affect his analysis.