- What follows below is the full text of the Introduction and Summary. I have divided it into the two sections indicated in the title.
- I have also added the occasional footnote1 of my own, and added links to whatever I have by the authors mentioned.
- It is also worth referring to:-
in order to see how Mellor’s thoughts have developed between the two versions of the book.
- "Mellor (D.H.) - Real Time II: Preface", and
- "Mellor (D.H.) - Real Time II: Introduction" in
- "Mellor (D.H.) - Real Time II",
Introduction (Full Text)
- This book is about such of the metaphysics of time as follows from settling the significance of tense, i.e. of the distinctions we draw between past, present and future. One way and another, tense covers most of time’s metaphysics, for its status is itself the main and most contentious metaphysical question about time, and on it depends much else besides:
All these matters will be settled in the course, or in consequence, of settling the status of tense.
- What makes tensed statements true or false;
- Our need for, and the nature of, tensed thought and speech;
- The fact that all our thought, action and experience takes place in the present;
- Our sense of time passing;
- How we perceive the temporal order of things and events;
- Our inability to perceive the future or affect the past;
- Time’s intimate connection with change;
- How time differs in this and other ways from space;
- How things differ from events;
- Why causes generally precede their effects and whether some might succeed them;
- The direction of time and of its passing from future to past;
- Whether time travel is possible;
- The peculiarly temporal character of prediction.
- Four metaphysical questions about time I shall not discuss:
These questions are too independent of tense, and too considerable, to be tackled with it in this book. The third and fourth turn too much on theoretical physics and cosmology, the second on how much the measurement of time depends on conventions, and the first and fourth on the logic of infinity.
- Whether time is continuous, dense or discrete;
- What makes different intervals of time the same or different in extent;
- Whether time is something over and above what happens in it;
- Whether time has a beginning or an end.
- Some philosophers think abstruse and debatable theories of physics or of meaning are also needed to solve the problems I shall tackle. I disagree, but instead of arguing my case abstractly, I would rather prove it passim by doing without them. I shall take note en passant of some seemingly relevant bits of physics and semantics, but only to show that they are either irrelevant or indisputable. It is for instance debatable whether, and if so when, statements about the past or future can be true or false; and in general how far saying in what conditions a statement would be true gives its meaning. But I need not take sides in either debate (although I shall incidentally settle the first). I need only the undoubted fact that whenever statements about the past or future are true or false, their truth or falsity is fixed, given their meaning, by how much earlier or later they are made than whatever they are about. (If ‘It will rain tomorrow’ is ever true, it is true the day before it rains.) It may similarly be debatable in relativistic physics whether causes always precede their effects absolutely, i. e. in all reference frames; but my proof that they do, while consistent with relativity, does not invoke it and is impervious to controversy about it. Generally, indeed, I refer to physics chiefly to dispel misapprehensions of its authority: over the direction of time, for example, or the distinctions I need to draw between time and space and between things and events in order inter alia to account for change.
- It is somewhat unfashionable nowadays to do metaphysics in English without relying on physics or the philosophy of language, and although I forgo the fashion, I am not trying to change it. Maybe metaphysics does mostly depend on physics and philosophy of language. But the metaphysics of time mostly does not; and that being so, there is value in tackling it my way. Steering clear of scientific and semantic debates makes my course not only safer but easier to follow, since I thereby avoid much needless technicality and jargon. That will help, I hope, to make time’s metaphysics more accessible to students and to the public, without burking any material difficulty in it: a desirable end, given the importance of time and the fascination it holds for most people. It is not an easy subject, but nor is it the preserve of physicists or purveyors of theories of meaning.
- I am of course in debt to much philosophical writing, old and new, about time and related matters. Among writers of this century, J. McT. E. McTaggart, Bertrand Russell, Albert Einstein, H. Minkowski, Hermann Weyl, C.D. Broad, R.B. Braithwaite, A.J. Ayer, W.V. Quine, Karl Popper, H. Reichenbach, J.C.C. Smart, Adolf Grunbaum, Hilary Putnam, John Earman, Richard Swinburne, J.R. Lucas, G.C. Nerlich, Anthony Quinton, Donald Davidson, Arthur N. Prior, Peter Geach, Richard Gale, J.L. Mackie, Michael Dummett, David Lewis, Richard Jeffrey, Lawrence Sklar, William Godfrey-Smith, W.H. Newton-Smith, Irving Thalberg and John Perry have all supplied or provoked more or less important parts of my argument. But although I list relevant works by these and other authors at the end of the book, I shall refer very little to them in the text. That is partly for the sake of readers unread in all this literature, and partly because its bulk, and the variety of its idioms, prevent my doing it justice succinctly and without obscuring the gist of the book. I must emphasise therefore that the fewness of my references is not meant as a sign of originality. On the contrary, its excuse is that my main points, albeit disputed, are so common in the literature as to be by now public property. So I trust no offence will be taken for or by authors whose work I use without acknowledgement.
- One author, however, I will acknowledge: J. McT. E. McTaggart, who proved the unreality of tense and of the flow of time. Although well known to philosophers, his proof has rarely had its due, and since it is the lynchpin of my book, I wish to make amends for that explicitly.
- This book in short is a self-contained, argued exposition of a view of time quite familiar to philosophers. It is not itself very original, nor is it a guide to what is. Its aim is simply to expound the view in plain terms, showing by consecutive argument how ramified its consequences are. There, if anywhere, lies its claim to be read; so, to fortify the claim, I will now outline the argument, whose structure might otherwise be veiled by the detail of ensuing chapters. But being more digest than preamble, what follows may be too condensed for readers new to the subject: if so, they should skip it now and return to it later.
Summary (Full Text)
- Everyone distinguishes past, present and future, and applies the distinction to everything that is in time at all: to people, animals and plants, to experiences, thoughts and actions, to inanimate things, events and processes, to dated facts about all these, and to dates themselves. We and contemporary animals, our and their activities and experiences, and the plants and other natural objects, happenings, facts and artefacts of our time were once future, will all eventually be past and are now present; whereas our remote ancestors and their times, once future and then present, are now past, while our remote descendants, who will in time become present and then past, are as yet still only future.
- The present, and temporal distances from it, past and future, I follow custom and call tenses. This sense of ‘tense’ relates of course to verbal tense, but the two must not be confounded. What I call tense need not be marked by modifying verbs. Not all languages use verbs to mark tenses, and even English verbs only differentiate past, present and future qualitatively, finer distinctions of tense being made by adverbs and phrases like ‘ten minutes ago’, ‘today’ and ‘next year’. To me it makes no odds how tenses are marked, so by ‘tensed’ statements and sentences I shall mean those that say, by verbal tense or otherwise, how near or far from the present, past or future, something is. By ‘tense’ I shall not mean verbal tense unless I say so.
- Distinctions and transitions of tense, between what has been, is and will be past, present and future, divide philosophers into two fundamentally opposed camps. The one, "tensed", camp takes these distinctions to reflect real nonrelational differences between past, present and future things (events, facts, etc.). By ‘non-relational’ I mean that an event’s being present when it occurs, its previously being future, and subsequently past, are supposed to be more than the unchanging relations all events always have to earlier, simultaneous and later times, viz, the tenseless relations respectively of being later, simultaneous and earlier than them. Futurity, temporal presence and pastness are all supposed to be real nonrelational properties which everything in time successively possesses, changing objectively as it exchanges each of these properties for the next.
- Tenses, in short, are supposed to be much like (e.g.) temperatures; and just as temperature differences make things differ in other ways, so for the tensed camp other differences depend on differences of tense. The camp is not indeed united on what else depends on tense. Some think existence does, so that only what is present exists, or only what is past or present, what is still only future being as yet non-existent. Others admit the future’s existence, but allow objectively possible alternatives to it which they deny to the present and the past, these being fixed and settled in some way that the future is not. But all such doctrines require real nonrelational differences between past, present and future for these other differences to depend on; and that is what we in the "tense-less" camp deny.
- The tenseless camp often offers only weak inducements to join it: the relative simplicity of tenseless logic, for example, or its consonance with relativity’s unification of space and time. But tenseless time needs a stronger sales pitch than that. Tense is so striking an aspect of reality that only the most compelling argument justifies denying it: namely, that the tensed view of time is self-contradictory and so cannot be true. McTaggart showed that in 1908, while trying to show time itself to be unreal. Time, however, is not unreal: the rest of McTaggart’s argument is wrong. But the incredibility of his conclusion has unfortunately also infected his disproof of tense, which is why the tensed camp still has members and needs a new presentation of McTaggart’s argument to empty it for good.
- By showing how time can be real though tense is not, I hope to escape the incredulity McTaggart met. And even about the unreality of tense I must enter a caveat. I am not saying that tense is subjective: for example, that to be present is to be present to consciousness or in some other such way without the scope of physics. Past, present and future tense statements — e.g. a clock saying (in effect) ‘It is now two o’clock’ by chiming twice — are objectively true or false quite independently of consciousness or of anything else subjective. Physical facts alone suffice to make them true or false. What makes a clock’s chiming two true, if it is, is its chiming two at two o’clock; and there is nothing subjective or psychological about that.
- But nor is there anything tensed about it. Like other specimens or "tokens" of present tense sentences, the chime is true if and only if it occurs at the same time as it asserts to be present, in this case two o’clock, whether that is now the present time or not. Similarly for tokens of future tense sentences, which are true if and only if suitably earlier than their subject matter: e.g. ‘The train will arrive in ten minutes’ is true just in case it is said ten minutes before the train arrives. Similarly for past tense tokens, true if and only if suitably later than their subject matter: ‘Today is the Queen’s fiftieth birthday’ is true if said fifty years after her birth and false otherwise. So far as time goes, in short, the truth of a tensed statement depends only on how much earlier or later it is made than whatever it is about. Whether its subject matter is also past, present or future is irrelevant to its truth2; so such statements can quite well be objectively true or false even though nothing in reality is past, present or future at all.
- The above means that I subscribe to the so-called "token-reflexive" account of what makes tensed statements true or false, an account which lets me keep objective tensed truths and falsehoods while rejecting objectively tensed things, events and facts. But the tensed camp deny that this can be all there is to tense, and in particular to our experience of tense. All the double chimes of an accurate clock, for example, are equally true because they occur at some two o’clock or other. But as we hear it chime, we know also that just one of these two o’clocks really is present, which none of the others is. Hearing the chime tells us that, because it is a fact of experience that all experience takes place in the present. This curious phenomenon, the experienced temporal presence of experience, is the crux of the tensed view of time, and the tenseless camp must somehow explain it away. I do so here by exploiting the token-reflexive account of what would make a simultaneous thought, ‘This experience is present’, true.
- Although I put the token-reflexive account of tensed truth to these tenseless uses, I have a caveat to enter about it too. I am not trying to give tenseless — i.e. non-token-reflexive — translations of tensed statements. That is easily shown3 to be impossible. Nor could we dispense with the states of tensed belief which they express, because to get what we want we have to act at more or less specific times. To catch the six o’clock news, for example, I must turn on the radio then, which in practice means that I turn it on when I believe it is six o’clock now. We need, that is, to act on beliefs true only at some times and not at others, i.e. on beliefs expressed by temporally token-reflexive and therefore tensed statements. Tense-less beliefs, true always if at all, could neither cause nor explain the timeliness of our actions unless accompanied by appropriately tensed beliefs.
- By showing how temporally token-reflexive thought and speech is both untranslatable and indispensable, I show why there are inescapable objective truths about what is past, present and future, even though nothing really is past, present or future in itself4. Although tense is not an aspect of reality, to us who act in time it is an inescapable mode of perceiving, thinking and speaking about reality.
- But what then distinguishes temporal from spatial token-reflexives? The thought or statement ‘Cambridge is here’, true only in Cambridge, is as token-reflexive as ‘It is now two o’clock’, as indispensable in its place, and as untranslatable into non-token-reflexive terms. What makes ‘It is now two o’clock’ tensed is not just that it is token-reflexive, but that to be true it needs to be thought or said neither earlier nor later than two o’clock, whereas ‘Cambridge is here’ needs to be said within the spatial bounds of Cambridge. But what makes earlier and later temporal as opposed to spatial relations? Or, to put the question another way: how does time differ from a dimension of space?
- The obvious answer is that time is the dimension of change. Motion, for example, is change of spatial location, i.e. being in different places at different times; and change in general is things having different properties from time to time. But things spread out in space can also have properties varying from place to place. A poker, for instance, can as readily be at once hot one end and cold the other as it can be all hot one day and all cold the next. Why is variation of its temperature across space not change when its variation through time is? It will not do to define change as variation through time, if time itself can only be defined as the dimension of change.
- Real tense provides an easy way out of this vicious circle. The tenses of things, events and facts, i.e. how far future, present or past they are, are constantly changing. This is the familiar flow or passage of time, and it is what distinguishes tenses from dates. A thing’s dates are permanent, its tenses are not: that is the obvious — and, as we shall see, the only — difference between them. Now, nobody believes in "spatial5 tenses", i.e. in any spatial "hereness" or "thereness" of places besides the token-reflexive facts which make ‘Cambridge is here’ true in Cambridge and false elsewhere. Consequently there is no spatial analogue of the passage of time, the ever-changing tense of things, events and facts moving inexorably from the far future through the present to the remote past. So if only this movement existed, it could be used to distinguish time from space, so that change could be defined as the temporal variation of a thing’s properties without begging the question against its spatial counterparts.
- But McTaggart has proved6 the passage of time impossible, so that account of change will not do. The way tenses would have to keep changing, to accommodate the token-reflexive facts that make tensed statements true or false, is what prevents them existing in reality at all. So how, if not by its passage, may time be distinguished from space as the dimension of change? McTaggart thought it couldn’t be, and hence that change, and therefore time itself, were unreal. And much of the tenseless camp concurs with him in substance, citing in support of time’s spacelikeness the spacetime of relativity, whose spatial and temporal components can be identified7 only arbitrarily. (It is no accident that relativity’s spacetime manifold is often taken to imply a changeless universe.)
- In fact relativity gives no reason to think time spacelike or the world devoid of change. On the contrary, it invokes in causation8 the very means we need to distinguish tenseless time from space. If one event affects another, it is absolutely earlier, i.e. earlier in all reference frames. Causal order fixes temporal order and thereby distinguishes it from spatial order. But can we say why without again invoking tenses?
- The answer lies in how temporal order is perceived. Suppose for example I see one event e precede another, e*. I must first see e and then e*, my seeing of e being somehow recollected in my seeing of e*. That is, my seeing of e affects my seeing of e*: this is what makes me — rightly or wrongly — see e precede e* rather than the other way round. But seeing e precede e* means seeing e first. So the causal order of my perceptions of these events, by fixing the temporal order I perceive them to have, fixes the temporal order of the perceptions themselves. And from this modest observation I can derive the universal dependence of temporal on causal order.
- This may seem in summary a devious and unlikely derivation, although I hope it will not seem so when carried out. But the striking fact it rests on should be noticed, namely that perceptions of temporal order need temporally ordered perceptions. No other property or relation has to be thus embodied in perceptions of it: perceptions of shape and colour, for example, need not themselves be correspondingly shaped or coloured. This sharing by a perception of the property thereby perceived is peculiar to time, and fundamental enough in my view to define it.
- With tenseless time thus defined9 by means of causation10, change can now be defined as variation through time. But not all variation through time is change, and to say what is and what is not, I must explain and exploit a familiar distinction. The distinction is between events on the one hand, and things, such as people, animals, plants and ordinary material objects, on the other. The explanation is that whereas both things and events may be extended in time as well as space, only events have temporal parts; things do not11. It was not just a temporal part of Everest that temporal parts of Hilary and Tenzing first climbed: both men and mountain were wholly present throughout all the temporal parts of that historic event.
- Change may now be defined as a variation in a real property of something, provided the variation does not reduce to a difference between different parts of it. Things therefore may change, but not events, since events’ properties varying through time always do reduce to different temporal parts having different properties. A concert, for instance, which starts quietly and gets louder simply has more or less loud temporal parts. But although events do not change, they may of course be changes, namely changes in things.
- This definition of change has obvious virtues, once we admit that change cannot really be different things and events successively becoming present and then past. The first is that it fits usage: we think of people, animals, plants and material objects as changeable; but not events, and in particular not changes. More important, it is intrinsically plausible. Two entities differing in their properties do not in general constitute change, because they supply no one entity that changes. Why make an exception just when one is later than the other and both are parts of something else (which, as a whole, has neither property)? Most important of all, the definition associates change exclusively with time. Spatial variation is not change12, because things and events whose properties vary simultaneously from place to place always have corresponding spatial parts to whose different properties the spatial variation reduces. A poker hot one day and cold the next thereby changes, because it is wholly present on each day; but a poker at once hot at one end and cold at the other is not wholly present at each end. Only parts of it are; the poker as a whole is therefore neither hot nor cold, and a fortiori does not change in that respect.
- Despite its manifest virtues, there are objections to this definition. On it, changes do not change, which McTaggart thought they had to do in order to be changes. But why must changes change? The idea is a non sequitur, and I just deny it. Some tidy-minded philosophers have also claimed (apropos especially of relativity) that things are really sequences of events13, which for me would mean there is no change. But I see no reason to believe this claim - certainly relativity gives none — and good reasons not to, if only because it groundlessly flouts usage and precludes the only tenable account of tenseless change.
- More interestingly, I must also deny the converse reduction, of events to changes in things. This could not be right anyway, because some events, especially in microphysics, are obviously not changes in anything. But even if they were, the reduction would not do. It would mean defining events as changes in real properties of things, and saying therefore why, e.g. being forty or famous is not a real property, since variation in those respects need not be a change at all. I need not change in any tenseless way on my fortieth birthday, nor when I unwittingly hit the headlines. And the reason is that these alterations in me need not be real events, i.e. need not have immediate effects in my vicinity. In short, for my definition of change to be credible, changes must be restricted to events, independently understood as producers of immediate contiguous effects, and not the other way round.
- So much for change through tenseless time; now for its direction. Being tenseless, its direction is not the difference between past and future, but that between earlier and later, which we have seen to be the temporal difference between cause and effect. That explains at once why we can affect some future events, i.e. events later than our actions. Moreover, since to see or otherwise perceive something is inter alia to be affected by it — e.g. by photons reflected from it to the eye — it also explains our ability to perceive some past things and events, i.e. events earlier than our perceptions of them. But our sense of the flow of time, from events being affectable to their being perceptible, remains to be explained, and so does our complete inability to perceive the future or affect the past.
- The flow of time is relatively straightforward. It turns out to be in reality no more than an accumulation of successive memories. That is, first I have an experience, then I remember having it, then I remember remembering it, and so on. Now memory is like perception in that a memory is an effect, direct or indirect, of what is remembered, and hence is always later in time. These successive memories of memories can therefore only accumulate at successively later, not earlier, times, and this is why our sense of the flow of time has the direction it has.
- It is harder to say why we cannot perceive the future or affect the past. What this comes to on my view is that we cannot affect what we have already perceived, i.e. one event cannot both affect and be affected by another. The question therefore is: why can causes and effects not form a closed loop in and via which each event indirectly affects itself? Only if this were possible could we affect the past (or perceive the future — it comes to the same thing), for example by travelling back in time, or could the whole universe form a complete temporal cycle, with all events both earlier and later than each other.
- That all this is impossible can be shown by extending an argument of Professor Dummett’s. The extended argument exploits the tact that causation14 is by definition the mechanism inter alia of both action and perception, but uses only the weakest possible assumption about it: namely, that a cause makes its effects more probable than in the circumstance they would otherwise have been. This must be so, for it would otherwise make no sense to perform an action for the sake of its effects, since performing it would not increase their probability; while if I would be just as likely to see something even if it never happened, my seeing it would be no evidence for its happening: and both these consequences are self-evidently absurd.
- From this undeniable assumption about causation15 it follows that enough similar causes will almost certainly produce a statistically significant correlation with their effects; conversely, that if there certainly is no such correlation, there is no causation16 either. Suppose we use this to test the idea of a closed causal loop, taking the loop to include an action, an effect of the action, and the perception of that effect. (This restriction is only to make it easier to visualise the experiment: it is not essential.) We consider therefore many such loops, trying to get the action performed in just half the cases where the effect has been perceived. If we succeed, there will be no correlation between the action and its supposed effect, and so no causation17 between them. We can only fail, however, if either the effect increases the probability of the action, in which case the causation18 is the wrong way round, or some of our perceptions turn out to have been wrong, i.e. some of the effects cannot really be perceived until after the corresponding actions have been done. But real events, it has already been remarked, all have contiguous effects, by which they could always be perceived somehow at the time. The only way an effect can be by no means perceptible before its cause is by not after all preceding it — but then there will again be no closed timelike, i.e. causal, loop from action to effect to perception and back to the action. So whatever happens the causes and effects will form no such loop; and that will be so whether they include actions and perceptions or not, since the argument depends essentially only on the statistics. The correlation which causation19 needs cannot be attributed to it all the way round a closed chain of events. That is why we cannot affect the past or perceive the future, why backward time travel is impossible, and why neither the whole universe nor any part of it can form a closed temporal cycle.
- I do not expect the summary of the last few pages, and perhaps especially of the last20 argument, to be immediately convincing on its own. (If it were, the rest of the book would be superfluous.) But that is not its function, which is to be part trailer, part summary of what follows. For the full truth about time and tense, now read on.
Footnote 1: Some of which may be removed or clarified if and when I read the book.
Footnote 2: But not to our knowledge of the truth value.
Footnote 3: Where does Mellor show this?
Footnote 4: That is, non-relationally.
Footnote 5: “Here” is obviously parochial, while “now” is not so obviously so. Yet Mellor probably thinks it’s also the parochial bias of the observer at that time.
Footnote 6: Well, this is Mellor’s claim, but has he really – even when Mellor has patched the argument up? See "Mellor (D.H.) - The Unreality of Tense".
Footnote 7: What does this mean? The time dimension is (mathematically) imaginary, in any case, in that durations have i = √-1 prefixed to them.
Footnote 9: Is time (tenseless or otherwise) something that can be “defined”?
Footnote 11: This is a bold claim, as it rules out MTP (the Metaphysics of Temporal Parts), espoused by Perdurantists and Exdurantists.
Footnote 12: But we do say that some demographic (house prices, say) changes as we move about the country.
Footnote 13: In SR, an event is an idealised point in space-time at which something happens. I doubt this gives any license to the identification of things with sequences of events – even if things are taken to be space-time worms.
Footnote 20: I’m glad to hear this, as I didn’t fully understand the argument.
Text Colour Conventions (see disclaimer)
- Blue: Text by me; © Theo Todman, 2018
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