- Before directly discussing the notion of the present, I want to discuss the notion of the real. These two concepts are closely connected; indeed on my view they are one and the same concept, and the present simply is the real considered in relation to two particular species of unreality, namely the past and the future. So let's begin with the real in general.
- Philosophers often speak as if the real world were just one of a number of different big boxes in which various things go on, the other boxes having such labels as 'the mind' or 'the world of Greek mythology'. For example, centaurs exist in the world of Greek mythology but not in the real world, aeroplanes exist in the real world but not in the world of Greek mythology, and horses and men exist both in the real world and in the world of Greek mythology. Again, Anselm addresses himself to people who held that God does not exist in the real world but only in the mind, and claimed to have a proof that if God exists in the mind he must exist in the real world too. Leibniz contrasted the real or actual world with an infinity of merely possible worlds in which various things happen which do not happen in the actual world. All these ways of talking suggest that the real world or the actual world is just a region of some larger universe which contains other regions as well - possible worlds, imaginary worlds, and so on.
- I want to suggest - I don't of course claim that there's anything original in this suggestion - that this way of conceiving the relation between the real and the unreal is profoundly mistaken and misleading. The most important way in which it is misleading is that it minimises, or makes a purely arbitrary matter, the vast and stark difference that there is between the real and every from of unreality. For talking of the real as one 'region' among others immediately suggests the question, 'In that case, what is so special about the real world in contrast with all other regions? - is it not a kind of narrow-mindedness and parochialism to think that it has anything special about it that none of the others have?' One philosopher, Meinong, has indeed said precisely that it is just narrow-mindedness and parochialism to single out the real world as a region of special interest; the 'prejudice in favour of the actual', he called it. Well, I want to argue that this is not just narrow-mindedness and parochialism, and that it becomes obvious enough what is so special about the real world as soon as we drop this metaphor of boxes or regions and become a little more literal.
- To say that there are centaurs in the world of Greek mythology is surely not to say that there are centaurs in some remote and peculiar region, but just to say that Greek myth-makers have said that there are centaurs. Similarly, to say that there are centaurs in some person's mind is to say that that person thinks or imagines that there are centaurs. And to say that there are possible worlds in which there are centaurs is just to say that it could be thatthere are centaurs. In general, to say that X is the case in some non-real world is just to say 'X is the case' with some modifying prefix like 'Greek myth-makers have said that', 'Jones imagines that', or 'It could be that'. But to say that X is the case in the real or the actual world, or that it is really or actually or in fact the case, is just to say that it is the case - flat, and without any prefix whatever. To say that there are centaurs in the real world, for example, is not to say that there are centaurs in some region of the universe in which we happen to have more interest than in others; it is simply to say that there are centaurs. Talk of the real world, in other words, is not a metaphorical fudging-up of talk in which our sentences have a special kind of prefix, but a fudging-up of talk in which the relevant sentences have no prefixes at all. 'Really', 'actually', 'in fact', 'in the real world' are strictly redundant expressions - that, and not any prejudice or provincialism, is their specialness.
- So to say that although there are no centaurs in the real world there are some in the world of Greek mythology, is just to say that although there are no centaur's Greek myth-makers have said that there are; to say that although God does not exist in reality he exists in the mind, is just to say that although God does not exist people may imagine that he does; to say that although Sextus raped Lucretia in the real world there is a possible world in which he didn't, is just to say that although Sextus raped Lucretia he need not have done so. There is, if you like, no other place than the real world for God or centaurs to exist in or for Sextus to rape Lucretia in; for God or centaurs to exist in the real world, or for Sextus to rape Lucretia in the real world, is just for God or centaurs to exist, or for Sextus to rape Lucretia. Again, 'Greek myth-makers have said that there are centaurs in the real world' is all one with 'Greek myth-makers have said that there are centaurs', and so is 'Greek myth-makers in the real world have said that there are centaurs.'
- And now the present. It is tempting to think of the present as a region of the universe in which certain things happen, such as the war in Vietnam, and the past and the future as other regions in which other things happen, such as the battle of Hastings and men going to Mars. But to this picture there is the same objection as to the picture of the 'real world' as a box or region among other boxes or regions. It doesn't bring out what is so special about the present; and to be more specific, it doesn't bring out the way in which the present is real and the past and future are not. And I want to suggest that the reality of the present consists in what the reality of anything else consists in, namely the absence of a qualifying prefix. To say that Whitrow's lecture is past is to say that it has been the case that Whitrow is lecturing. To say that Scott's lecture is future is to say that it will be the case that Scott is lecturing. But to say that my lecture is present is just to say that I am lecturing – flat, no prefixes. The pastness of an event, that is to say its having taken place, is not the same thing as the event itself; nor is its futurity; but the presentness of an event is just the event. The presentness of my lecturing, for instance, is just my lecturing. Moreover, just as a real thought of a centaur, and a thought of a real centaur, are both of them just a thought of a centaur, so the present pastness of Whitrow's lecture, and its past presentness, are both just its pastness. And conversely, its pastness is its present pastness, so that although Whitrow's lecture isn't now present and so isn't real, isn't a fact, nevertheless its pastness, its having taken place, is a present fact, is a reality, and will be one as long as time shall last.
- Notoriously, much of what is present isn't present permanently; the present is a shifting, changing thing. That is only to say that much of what is the case, of what is real and true, is constantly changing. Not everything, of course; some things that are the case also have always been the case and will always be the case. I imagine scientists have a special interest in such things. And among the things that not only are the case but always have been and always will be, are the laws of change themselves, I mean such laws as that if anything has occurred then for ever after it will have occurred (like Whitrow's lecture). These are the laws of what is now called tense logic, and the conception of the present that I have just been suggesting is deeply embedded in the syntax of that discipline. So that conception underlies, or anyhow seems to underlie, what is now a pretty flourishing systematic enterprise2. Precisely for this reason, it seems to me important that we tense-logicians should realise that there are difficulties about this conception of the present, arising either from physical science or from the philosophy of physical science. So I want now to state as clearly and crudely as I can what this difficulty appears to be.
- Suppose we have observed on some very distant body a regularly repeating process of some sort, say a pulsation. We have just observed one of these pulsations, and as the body is a very distant one, we know that the pulsation we are observing happened some time ago. We now consider the pulsation immediately after the one we are observing, and we ask whether this next pulsation, although we won't of course observe it for a while, is in fact going on right now, or is really still to come, or has occurred already. On the view of presentness which I have been suggesting, this is always a sensible question. At least if there are to be any further pulsation at all, then either the body is pulsating, or it is not the case but will be the case that it is pulsating or it is not the case but has been the case that it is pulsating. The difference between pulsating — really and actually pulsating — and merely having pulsated or being about to pulsate, is as clear and comprehensible a difference as any that we can think of, being but one facet of the great gulf that separates the real from the unreal, what is from what is not. Just this, however, is what the special theory of relativity appears to deny. If the distant body is having its nth pulsation as we perceive it having its n-1th — is pulsating, and not merely has been or will be pulsating — then the nth pulsation and the perception of the n-1th are simultaneous; not just simultaneous from such and such a point of view or in such and such a frame of reference, but simultaneous. And according to the special theory of relativity, such "absolute" simultaneity is in many cases just not to be had3.
- One possible reaction to this situation, which to my mind is perfectly respectable though it isn't very fashionable4, is to insist that all that physics has shown to be true or likely is that in some cases we can never know, we can never physically find out, whether something is actually happening or merely has happened or will happen. I'm sure there are questions which are perfectly genuine5 and intelligible questions but which seem to be incapable of being answered. For instance, I know perfectly well what it would be for you to see what I would call purple wherever I see red, and for you to see what I would call blue wherever I see purple, and so on round the clock; but I cannot imagine any procedure which would conclusively show that our respective visual experiences are, or that they are not, related in this way. And there may well be a similar but more subtle systematic impossibility in finding the answer to questions like my one about the distant pulsating body.
- Furthermore, when confronted with unanswerable questions, it is often good scientific practice to devise a language in which these questions cannot be even asked. And this usually involves a good deal more than just refraining from admitting certain words or longer expressions into one's scientific vocabulary; the very syntax of scientific language will be involved too. As far as our present subject is concerned, even before Einstein physical scientists not only eschewed the words "past", "present" and "future", but eschewed tenses too. Time enters physical science through intervals by which one event may be earlier or later than another. Whether the events are the case or merely have been or will be, is of no concern to the scientist, so he uses a language in which the difference between being and having been and being about to be is inexpressible. And this, as I've said, has been the case since long before the special theory of relativity. That theory, all the same, has made an important difference. Before it was devised, the relation between tensed language and the tenseless language of the scientist was pretty straightforward. It amounted to this: When a scientist said "The interval between an earlier event A and a later event B is n time units", you could translate this as "It is or has been or will be the case that (B is occurring and it was the case n time units ago that (A is occurring))". But I don't think this is what a scientist now means by "earlier" and "later", and indeed a scientist is not now likely even to say that the interval between A and B is n time units, just like that; the only interval between a pair of events to which he will give a definite value is a space-time one.
- The original paper is A. N. Prior, 'The Notion of the Present', Studium Generale, 23 (1970), pp. 245-8.
- The Van Inwagen & Zimmerman extract cuts off here.
- Probably for good reason, as the paper seems to go off the rails from hereon in.
- This sounds a bit muddled up to me. There’s no such thing as absolute simultaneity in SR. It all depends on the frame of reference.
- Probably because it’s off target. This case has nothing epistemological about it.
- Well, I agree, but the logical positivists didn’t.
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