‘For what is time? Who can easily and briefly explain it? Who even in thought can comprehend it, even to the pronouncing of a word concerning it? But what in speaking do we refer to more familiarly and knowingly than time? And certainly we understand when we speak of it; we understand also when we hear it spoken of by another. What, then, is time? If no one ask of me, I know; if I wish to explain to him who asks, I know not.’—Augustine, Confessions 11.14.17
How should we respond to Augustine’s perennial question? Rather than considering Augustine’s own response, I would like to consider an influential response due to the early 20th century idealist philosopher, J.M.E. McTaggart. I say that his response was influential, but that is not strictly accurate: his answer was to claim that time is unreal, and that has not proved a popular position in the contemporary philosophy of time. His discussion of what time must be like if it were real, however, has been very influential indeed, and has shaped the contemporary debate ever since.
McTaggart claimed, like many others before him, that time must, of necessity, involve change; but he also delineated two different ways of specifying, or determining, positions in time, and claimed that both of these ways are also essential to time. These delineations are widely regarded as an original contribution to the philosophy of time, and discussion of them has dominated the literature since McTaggart introduced them in 1908.
According to McTaggart, positions in time are determined either by—what he called—the A series or the B series. The A series is simply the ordering of events according to past, present, and future. So, the event of my typing this blog post is present, while the event of my having breakfast this morning is past, and the event of my having my dinner this evening is future. But when I was having my breakfast, that event was present and my typing this blog post was future. Soon that event will be past, and my breakfast will be a little more past, and my dinner will be a little less future (until it eventually becomes present). Obviously, the point here is that the A series is constantly changing with respect to which determinations apply to which events. And so, according to McTaggart, the A series gives us the change that is essential to time.
However, there is another way to order events in time, which is also essential to our concept of time, even if it is not as fundamental as the A series (we will see why shortly). This other way is the B series, and this series orders events according to the relations of earlier than and later than. So my breakfast is earlier than this blog post, and my dinner is later than this blog post. Notice, though, that these determinations never change. It is always the case that World War II is earlier than the first mission to the moon. This was true a million years ago and will be true a million years from now. Similarly, if the first manned mission to Mars is later than World War II, then this relation never changes. So the B determinations are fixed and static, and this is why McTaggart thinks they are not as fundamental to time as the A series, since they cannot allow for change (and the latter is required for time).
So the picture of time the A and B series offer us together is one of a fixed ordering of events along a timeline (the B series), with the ever changing ‘spotlight’ of the present moving along the timeline in the direction of the future (giving us the A series). This picture certainly is evocative of our concept of time, but there is a problem. The problem, according to McTaggart, is that the A series is inherently self contradictory, and therefore cannot be real (since reality cannot tolerate contradiction); and if the A series is not real, then there can be no time (since the B series alone cannot account for change).
Why think that the A series is self contradictory? Well, consider that past, present and future are incompatible determinations: ‘e is past’ implies that ‘e is neither present nor future’, and so on. But every event admits of all three incompatible determinations. What is past, has been present and future. What is present, will be past and has been future. What is future will be present and past.
No doubt you’ll be smirking at this apparent sophism, and thinking, ‘Well, obviously, events are past, present and future at different times. E is never past, present and future.’ And this does seem right, since, as we just noted, when e is present, it will be past and has been future, or when it is past, it has been present and has been future, or when it is future, it will be present and will be past.
Naturally, of course, McTaggart anticipates this response. He counters by claiming that ‘will be past’ means ‘is past in the future’, and ‘has been future’ means ‘is future in the past’, and ‘has been present’ means ‘is present in the past’, and ‘has been future’ means ‘is future in the past’, and ‘will be present’ means ‘is present in the future’, and ‘will be past’ means ‘is past in the future.’ So what we are, in effect, doing here is compounding the three tenses in order to avoid the contradiction. (The three basic tenses will be compounded as ‘is past in the present’, ‘is present in the present’, and ‘is future in the present’.)
So, now we have nine complex tenses rather than three basic tenses, but is the problem solved? NO, according to McTaggart, because all events will admit of all nine tenses, and some are incompatible: ‘is past in the future’, for example, is incompatible with ‘is present in the past.’ If we now try to avoid the contradiction by compounding the tenses again, (i.e. ‘no event is past in the future and present in the past, rather an event which is present in the past, will be past in the future’), we end up with 27 tenses, and of course all events admit of these tenses, and some are incompatible! So, McTaggart claims, we are faced with a regress that is vicious, because every time we try to avoid the contradiction by compounding the tenses, the contradiction simply reappears at the next level of compounding.
Thus the A series is contradictory and therefore unreal, and so, then, is time.
Well, that’s McTaggart’s argument for the unreality of time. Almost no one working in the contemporary philosophy of time thinks that McTaggart’s conclusion is correct, but most think he was on to something important—although they disagree vehemently about what that was. So where do you think his argument goes wrong (assuming that you do think that)?