Time
In thinking about ‘now’ there is a temptation to regard it as a point or line dividing the past from the future. Trying to grasp the ‘now’ seems to be impossible because the very act of doing this is temporal – one is moving out of the ‘now’ as one does it, into a new ‘now’ which is in fact in the future of the ‘now’ one is trying to grasp, thus rendering that ‘now’ something past. On the other hand, giving ‘now’ sufficient duration to make it graspable, such that it is neither past nor future – the ‘specious present’ (an idea developed by E. R. Clay [E. R. Kelley] and William James) seems to introduce the idea that events perceived ‘now’ are both simultaneous qua belonging to ‘now’ and successive qua being events (i.e. qua occurrences in time) – an apparent paradox. But is it?
An escape from the puzzles here is to regard all time as ‘now’, with past and future as abstractions from it. Thus, ‘now’ is the complex of ‘what is’, conceived as embodying change and motion as its properties, with explanations of change and motion themselves requiring the abstractions of past and future to conceptualise what they consist in, viz. as movements from a past place or condition into a future place or condition – not relative to ‘now’ since they are speciously compresent in the ‘now’ but relative to an abstract point (which may or may not coincide with the ‘now’) from which the future is the future of a past. The experience of ‘now’ might be the experience of a stasis, but equally of change and motion, the dynamics of which are apprehended (grasped, appreciated as change or motion) as a whole.
It is a commonplace of temporal experience that subjective perceptions of the passage of time differ. The same event that pleases one person but bores her companion (an evening at the opera, perhaps) can go like a flash to the former but take excruciatingly long to the latter.[1] To coordinate subjectively different lengths of time to each other, public time is established by reference to regular saliences observable to all – the daily passage of the sun, the monthly phases of the moon. Because measurements based on the sun and moon are approximate and they fluctuate – the length of days varies with the seasons, lunar months do not fit exactly to the solar year– a more accurate system is necessary.[2] Public time is now measured precisely by atomic clocks, one second in SI units defined as the period in which a Caesium-133 atom oscillates.[3]
The prescriptive nature of public time is well exemplified by the history of railway timetables. In Britain the Mean Times of Bristol and Cardiff were respectively 10 minutes and 13 minutes behind Greenwich Mean Time (GMT), so in 1847 the Railway Clearing House adopted GMT as standard for the network; by the mid-1850s almost all public clocks in the kingdom were set to GMT and in 1880 Parliament established GMT as the official national standard. It accordingly became the international benchmark because of the geographical extent of British imperial possessions. This is stipulative public time. But the advance from subjective to public time, however precisely the latter is defined, does not yield ‘objective’ or ‘absolute’ time of the kind assumed by Newton (time as an ‘empty container’ existing independently of events within it). Locke postulated that absolute time is conceived by extrapolating indefinitely forward and backwards from public time, but as the adverb itself implies, this does not yield absolute time (nor, which is different again, infinite time) but only indefinite time – a temporal series without identifiable limits fore or aft.[4] Clarke, in the correspondence with Leibniz, defended the Newtonian conception against Leibniz’s relational view (time as a linear and anisotropic ‘order of successions’).[5] In all these cases the assumption at work is that ‘time’ is a univocal concept susceptible to definition as such.
But the widening difference in subsequent debates between philosophical attention to temporal phenomena – time as experienced – and physical theory is marked. Such notions as Bergsonian ‘duration’ and the idea of the ‘specious present’ address the subjective experience of time, while the absorption of time into Minkowski space in which time is the fourth dimension of a continuum (taking ‘dimension’ to refer to the smallest number of coordinates required to locate a point in a mathematical space) serves the purposes of the general theory of relativity’s account of gravity. Suggested by the conception of spacetime as a continuum, such notions as ‘spacetime worms’ (the path of an individual entity through the continuum), perdurantism and ‘temporal parts’, and conceptions of universal time such as the Block and Growing Block theories, have been predictable developments. On the Block Universe view, all times (past, present and future) exist together; on the Growing Block view, past and present are real but the future does not yet exist – or more accurately: that the future is open, and its becoming present and past consists in the progressive accumulation of existents.[6]
These competing views turn on the choice of a specified conception of time, once again as if ‘the concept of time’ is univocal in each and such that the preferred definition – time as eternal, or as a moving one-directional arrow, as explicable via the concept of entropy, as a set of relations, as a dimension of a continuum – makes independent sense. The purpose here is not to assess the merits of competing theories of this kind, philosophical or physical, but to note that no univocal conception is available in the conceptual scheme to serve as its privileged source. This is because how temporal concepts function in the scheme exhibits a variety in ways of being interpreted and applied. As structural features of the scheme, the differences in the uses made of temporal concepts – subjective, public, objective, physical – are ineliminable and mutually irreducible by anything other than an incomplete reduction. This is shown by the complexity of relations between subdiscourses of time, something well illustrated by the McTaggart argument.[7]
McTaggart took his argument to establish the unreality of time. Instead it shows that different ways of talking about the place and order of events in time address different interests we have in employing such talk. A-series concepts (past, present, future) presuppose the idea of change and accord naturally with dynamic conceptions such as the Growing Block theory; utterances attributing temporal location are tensed, and their truth-values change according to when they are indexed. B-series concepts (earlier, later) are applied in tenseless utterances, retain their truth-values eternally, and accord naturally with a Block Universe conception. McTaggart took the A-series to be fundamental – the B-series being insufficient because static, omitting the essential element of change – and yet inconsistent because all three properties of being past, being present and being future apply to all events, yet no two can belong to any event together.
The alleged inconsistency of the A-series vanishes when it is recognised what work the B-series does in the truth-condition for utterances in which one of the A-series properties is predicated. Possession of a truth-value by an A-property-predicating statement requires fulfilment of a presupposition, viz. security of a reference point in time in relation to which the predication applies in B-series terms, viz. earlier or later, thus: the statement ‘event e happened in the past’ can itself only be true or false if it is true that the time of its utterance e is later than the event in question. And likewise, mutatis mutandis, for the other properties. In this way the A-series is parasitic on the B-series, a point in any case obvious: the only way to explain the relations between the A-properties themselves is by saying how they stand in B-series terms with respect to each other.
The point generalises to tenses themselves. Take the categories of the Latin conjugations as a simple model: present (I run), future (I will run), imperfect (I was running), perfect (I ran), future perfect (I will have run), pluperfect (I had run). For the future perfect and the pluperfect, B-series concepts are essential: ‘I will have run’ applies to a point in time x after an earlier point in time y which latter is itself later than the time of utterance, while ‘I had run’ applies to a point in time x before a later point in time y itself earlier than the time of utterance. Obviously, talk of the future relates to a time or times later than the time of utterance. Less obviously but arguably, the B-series is involved in aspect also (as involved in the imperfect and perfect tenses, respectively denoting durations incomplete and completed) in at least the sense that in both not only is reference made to a time earlier than the time of utterance, but in what manner the event bears that relation to the time of utterance.
Asymmetry in the application of B-series concepts to the A-series enters with the present: the present is neither earlier nor later than any given time other than itself but a defining combination of these, reciprocally requiring the A-series: any ‘now’ is earlier than any future relative to it, later than any past relative to it. Given that attempts to define ‘now’ typically concede to the intuition that any moment has duration such that anything intelligibly describable as ‘now’ comprehends some moving fraction of past and future within it (the more so because all uses of ‘now’ are context-dependent; they can refer not just to a present moment but, say, to the present year or decade), the claim that B-dependent A-series concepts are at work here too is irresistible.
Another and fuller way to analyse the relativity of tenses is to employ the contrast drawn by Reichenbach and elaborated by Comrie between ‘speech time’, ‘event time’ and ‘reference time’,[8] while the further complexities of expressions turning on uses of ‘next’, ‘since’, ‘until’, ‘began’, ‘finished’, ‘simultaneous’, ‘during’, reference to instants and periods, and problems about the truth-value of future-tensed statements (Aristotle’s sea-battle), receive detailed examination both in discussions of temporal logic and in metaphysics.[9] The wealth of insights in these debates is great; here the focus is exclusively on the fact that the dominating factor in the conceptual scheme’s array of temporal concepts is utility, such that on some occasions reference is made to an instant and on others to a period, on some occasions precisely and on others vaguely (think of uses of ‘simultaneous’, ‘after’) – in general, communicative intention and context enter essentially into the interpretation of a temporal term’s application on an occasion, such that (for example) ‘then’ in ‘it happened then’ could refer to an instant or a century, ‘at the same time’ to an exact coincidence in time or in the course of a century – and so on.
If these points are implied by the simpler case of the connection between A-series and B-series concepts as discussed above, they apply a fortiori to the more elaborate cases considered in the metaphysical and logical debates mentioned. But accepting – if one does – that one cannot explain the terms of the A-series without reference to the B-series turns out to be not yet the whole story, for the difference in their respective manner of possessing truth-value is significant. The observation that statements predicating A-series properties change in truth value with changes in temporal standpoint whereas B-series predications have their truth-values eternally, registers an important feature of their respective places in cognitive economy. In marking a difference between an A-series task of ascribing an order to events relatively, the order in question being temporary, and the knowledge in B-series terms that events are ordered as earlier or later absolutely, entails a difference in the logical properties of knowledge claims involving temporal reference. The two cases differ crucially in that to know p in the A-series case requires knowing something else q specifically about the temporal location relevant to the subject-matter, whereas knowing p in the B-series case presupposes no such thing. Occupancy of different positions in inferential frameworks is a significant matter, given that in varying according to how temporal relations are referenced the truth-conditions of tensed and untensed assertions require respectively independent mastery. A typical set of assumptions is that statements about the past have definite truth-value, those about the future have none, while those about the local and immediate present pose a challenge as to choice of treatment: either they are always in effect statements about an immediate past, viz. the verifying or confirming just-current ground for assignment of truth-value (even when ‘the present’ is an extended period – this year, this decade – with the ‘immediate’ past being extended accordingly), or they are vague, and the question of their truth-value, or whether they have one at all, falls into the in-tray of problems about vagueness.
If grasp of the meaning of sentences in the language consists in or at least essentially involves grasp of truth or assertibility conditions, then mastery of future-tensed discourse can be represented in possible-worlds terms as a disjunction of determinately true versions and determinately false versions distributed across selected worlds. This avoids accepting truth-value gaps for future-tensed statements, but introduces a further ineliminable asymmetry between them and past-tensed statements, which apply to a single world – the actual one – and have a determinate truth-value, and present-tensed statements, with the problematic choice about them just described. In connection with the ad hoc nature of the scheme, the implication to be noted is that to learn to talk of time is accordingly to learn more than one subdiscourse of time in which different rules apply.
Moreover, the different ways of talking about time are not coterminous in their applications beyond talk of time-relations. For a chief example, the B-series plays an important role in causal thinking, but the A-series does not. The causal relation is dynamic, takes place in or over time, but the temporal relations between causes and effects are strictly B-series (including ‘simultaneous’ in the series, convenient for cases where cause and effect are held to occur together).[10] What this shows is that the difference between the concepts in the two series does not demonstrate the ‘unreality of time’ as if ‘time’ denoted a postulated single something shown by these considerations to be non-existent, but rather the relation (to employ the toolkit metaphor again) of different tools: in this case, rather aptly, a spanner and a screwdriver – for they can be used together, a spanner holding a bolt firm as a screwdriver is used to insert a screw into it (e.g. the dependence of the A-series concepts on the B-series concepts: ‘present is later than past, earlier than future’), but each of them having independent uses besides (e g. A-series and change, B-series and causation. Note that causal events involve change, but statements about causal nexuses are about a change).
Another important consideration is the intimate connection between conceptions of space and time in which the latter depends in essentially metaphorical ways on the former. It is a commonplace that distances are expressible in temporal terms – ‘the airport is thirty minutes away’ – when citing the geographical distance alone has nugatory informative content, given that fifteen miles on a desert road and fifteen miles from a city centre to an airport are very different matters. The description of the distance as effective distance in the city context requires reference to time to be useful, while reference to time is inessential in the desert road case. Whereas here space is being described in temporal terms, the reverse occurs with complete generality in speaking of time intervals as lengths – ‘long’ and ‘short’ – and in inferring the significance of more explicit measures of time: one minute is a short period of time relative to a century, a long period of time in the dental chair.
The primary signification of ‘length’ is a spatial extent between points in space; in dictionary definitions – reports of usage – the application to time is pertinently given as secondary or derived. Moreover judgments of the length of periods of time turn on the idea of spatial occupancy; a period of time containing little individual incident is described on a line in a shorter message than one that describes on a line a period crammed with incident – for example: contrast accounts of the period from the beginning of settled agriculture in the Neolithic era, about 10,000 BCE, to the ‘rise of civilization’ in Sumer after 4000 BCE, with accounts of the period from the latter date to the Bronze Age Collapse in 1200 BCE. The message on a line representing the former period is very considerably shorter than that representing the latter period, for the reason that greatly more is known about the latter period. (Use of the term ‘message’ here borrows from discussions of the contrast between simplicity and complexity, in which the length of message is one way of distinguishing between the two.[11]) Visualise a timeline along which the segment lengths are proportional to the quantity of information available for each point; like one of those representations of the human body proportioned to the degree of sensitivity to the physical environment showing enormous hands and lips, the timeline would for some periods represent many centuries as a short segment and individual decades as very long, thus representing the way time is viewed – how history is experienced, one could say, consistently with both a Block and a Growing Block perspective on it – as a space occupied by events.
For the purposes here the significant point is the irreducibility of the spatial metaphor in deployment of temporal concepts; all times are durations of some proportion (leaving aside the idealisation of a ‘point-instant’) and descriptions of durations essentially employ the spatial metaphor which applicable variants of ‘length’ such as ‘extent’, ‘expanse’, ‘sweep’ and ‘stretch’ – consider also ‘long ago’, ‘far off’, ‘close’, ‘near’, and the spatial connotation of ‘immediate’ – not only do not disguise but reinforce. We use the space-based concept of motion to speak also of events in time ‘approaching’, ‘moving’, ‘standing still’.
To revert to the initial suggestion that the basal experience of time is experience of ‘now’ one can profit from the spatial metaphor to suggest this: that experience in a ‘now’ is like looking a picture, in which the elements are dynamic and experienced as dynamic – that is, changing and moving – and which nevertheless one sees as a whole in the same Augenblick. I take it that this is what Clay and James were trying to get at with the notion of speciosity. Two related points need to be made in conjunction with it: that this is time as experienced (and thus is a form of intuition in Kant’s sense) and implies a Block Universe conception in which, however, the universe is accordingly phenomenal. The irreducibly of metaphor in the account of time in any case implies its artifactual nature as a concept - that is, as constructed to serve the evolved interests of creatures with human sensory and conceptual endowments, and hence as neither a compete nor a definitive account of objective reality - whatever that is.
[1] In this connection one can adduce considerations about distortions in perception of the passage of time, such as the Alice in Wonderland Syndrome; see Weissenstein et. al. Journal of Paediatric Psychiatry 2014.
[2] The solar year is 365.24219 days, the lunar month 29 days, hence the reason for calendar months being 30 or 31 days except for February at 28 days, extended to 29 every leap year to adjust for the drift of the calendar from the solar year.
[3] In the period its activity (at its ground state) defines, Caesium-133 oscillates slightly over nine billion times, giving an accuracy to within 1/15 billionth of a second per year. At an MIT lab it has been proposed that vastly more precise measurements can be obtained by entangling several hundred ytterbium atoms, which vibrate 100,000 times faster than caesium.
[4] See Locke, John, An Essay Concerning Human Understanding II.xv.5 (1689)
[5] See Clarke, Samuel The Leibniz-Clarke Correspondence ed. H. G. Alexander Manchester University Press 1956. Though a significant part of this debate relied on theological considerations, the use made by Leibniz of his Principle of Sufficient Reason – which Clarke accepted – and the Identity of Indiscernables retains a live interest.
[6] For a way into the predictable complexification of debate about the Growing Block view see Roberto Loss ‘Open Future, supervaluationism and the growing-block theory: a stage-theoretical account’ Synthese 199 (2021).
[7] McTaggart, J. M. E. "The Unreality of Time", Mind 17: 457–73; reprinted in McTaggart, The Nature of Existence, Vol. 2 (Cambridge: Cambridge University Press: Book 5, Chapter 33) 1927.
[8] Reichenbach, H., 1947, Elements of Symbolic Logic, (New York: Dover Publications, Inc. Ch 6 passim); Comrie, B., 1985, Tense, (Cambridge: Cambridge University Press.)
[9] A window into the extensive literature is provided by the two volumes of Blackburn, P., P. Hasle, and P. Øhrstrøm (eds.), 2019, Logic and Philosophy of Time Aalborg: (Aalborg University Press); Callender C. The Oxford Handbook of the Philosophy of Time (Oxford University Press 2013).
[10] Huemer M. and Kovitz B. ‘Causation as Simultaneous and Continuous’ Philosophical Quarterly 53 (2003) 556-65.
[11] A competing way is length of evolutionary history; something might be simple by one measure and complex by the other, as one sees on considering a pebble on a beach which has a simple smooth round shape because of a long formation by wave action – a short message describes the shape, a long message describes the process by which the pebble acquired the shape.