• originally from Key Writings

There is no doubt but that for us time is at first identical with the continuity of our inner life. What is this continuity? That of a flow or passage, but a self-sufficient flow or passage, the flow not implying a thing that flows, and the passing not presupposing states through which we pass; the thing and the state are only artificially taken snapshots of the transition; and this transition, all that is naturally experienced, is duration itself. It is memory, but not personal memory, external to what it retains, distinct from a past whose preservation it assures; it is a memory within change itself, a memory that prolongs the before into the after, keeping them from being mere snapshots and appearing and disappearing in a present ceaselessly reborn. A melody to which we listen with our eyes closed, heeding it alone, comes close to coinciding with this time which is the very fluidity of our inner life; but it still has too many qualities, too much definition, and we must first efface the difference among the sounds, then do away with the distinctive features of sound itself, retaining of it only the continuation of what precedes into what follows and the uninterrupted transition, multiplicity without divisibility and succession without separation, in order finally to rediscover basic time. Such is immediately perceived duration, without which we would have no idea of time.

How do we pass this inner time to the time of things? We perceive the physical world and this perception appears, rightly or wrongly, to be inside and outside us at one and the same time; in one way, it is a state of consciousness; in another, a surface film of matter in which perceiver and perceived coincide. To each moment of our inner life there thus corresponds a moment of our body and of all environing matter that is 'simultaneous' with it; this matter then seems to participate in our conscious duration.2 Gradually, we extend this duration to the whole physical world, because we see no reason to limit it to the immediate vicinity of our body. The universe seems to us to form a single whole; and, if the part that is around us endures in our manner, the same must hold, we think, for that part by which it, in turn, is surrounded, and so on indefinitely. Thus is born the idea of a duration of the universe, that is to say, of an impersonal consciousness that is the link among all individual consciousnesses, as between these consciousnesses and the rest of nature. Such a consciousness would grasp, in a single, instantaneous perception, multiple events lying at different points in space; simultaneity would be precisely the possibility of two or more events entering within a single, instantaneous perception. What is true and what illusory, in this way of seeing things? What matters at the moment is not allotting it shares of truth or error but seeing clearly where experience ends and theory begins. There is no doubt that our consciousness feels itself enduring, that our perception plays a part in our consciousness, and that something of our body and environing matter enters into our perception. Thus, our duration and a certain felt, lived participation of our physical surroundings in this inner duration are facts of experience. But, in the first place, the nature of this participation is unknown, as we once demonstrated; it may relate to a property that things outside us have, without themselves enduring, of manifesting themselves in our duration in so far as they act upon us, and of thus scanning or staking out the course of our conscious life. Next, in assuming that this environment 'endures', there is no strict proof that we may find the same duration again when we change our surroundings; different durations, differently rhythmed, might coexist. We once advanced a theory of that kind with regard to living species. We distinguished durations of higher and lower tension, characteristic of different levels of consciousness, ranging over the animal kingdom. Still, we did not perceive then, nor do we see even today, any reason for extending this theory of a multiplicity of durations to the physical universe. We had left open the question of whether or not the universe was divisible into independent worlds; we were sufficiently occupied with our own world and the particular impetus that life manifests there. But if we had to decide the question, we would, in our present state of knowledge, favour the hypothesis of a physical time that is one and universal. This is only a hypothesis, but it is based upon an argument by analogy that we must regard as conclusive as long as we are offered nothing more satisfactory. We believe this scarcely conscious argument reduces to the following: All human consciousnesses are of like nature, perceive in the same way, keep in step, as it were, and live the same duration. But, nothing prevents us from imagining as many human consciousnesses as we please, widely scattered through the whole universe, but brought close enough to one another for any two consecutive ones, taken at random, to overlap the fringes of their fields of outer experience. Each of these two outer experiences participates in the duration of each of the two consciousnesses. And, since the two consciousnesses have the same rhythm of duration, so must the two experiences. But the two experiences have a part in common. Through this connecting link, then, they are reunited in a single experience, unfolding in a single duration which will be, at will, that of either of the two consciousnesses. Since the same argument can be repeated step by step, a single duration will gather up the events of the whole physical world along its way; and we shall then be able to eliminate the human consciousness that we had at first laid out at wide intervals like so many relays for the motion of our thought; there will be nothing more than an impersonal time in which all things will pass. In thus formulating mankind's belief, we are perhaps putting more precision into it than is proper. Each of us is generally content with indefinitely enlarging, by a vague effort of imagination, his immediate physical environment, which, being perceived by him, participates in the duration of his consciousness. But as soon as this effort is precisely stated, as soon as we seek to justify it, we catch ourselves doubling and multiplying our consciousness, transporting it to the limits of our outer experience, then, to the edge of the new field of experience that it has thus disclosed, and so on indefinitely - they are really multiple consciousnesses sprung from ours, similar to ours, which we entrust with forging a chain across the immensity of the universe and with attesting, through the identity of their inner durations and the contiguity of their outer experiences, the singleness of an impersonal time. Such is the hypothesis of common sense. We maintain that it could as readily be considered Einstein's and that the theory of relativity was, if anything, meant to bear out the idea of a time common to all things. This idea, hypothetical in any case, even appears to us to take on special rigor and consistency in the theory of relativity, correctly understood. Such is the conclusion that will emerge from our work of analysis. But that is not the important point at the moment. Let us put aside the question of a single time. What we wish to establish is that we cannot speak of a reality that endures without inserting consciousness into it. The metaphysician will have a universal consciousness intervene directly. Common sense will vaguely ponder it. The mathematician, it is true, will not have to occupy himself with it, since he is concerned with the measurement of things, not their nature. But if he were to wonder what he was measuring, if he were to fix his attention upon time itself, he would necessarily picture succession, and therefore a before and after, and consequently a bridge between the two (otherwise, there would be only one of the two, a mere snapshot); but, once again, it is impossible to imagine or conceive a connecting link between the before and after without an element of memory and, consequently, of consciousness.

We may perhaps feel averse to the use of the word 'consciousness' if an anthropomorphic sense is attached to it. But to imagine a thing that endures, there is no need to take one's own memory and transport it, even attenuated, into the interior of the thing. However much we may reduce the intensity of our memory, we risk leaving in it some degree of the variety and richness of our inner life; we are then preserving the personal, at all events, human character of memory. It is the opposite course we must follow. We shall have to consider a moment in the unfolding of the universe, that is, a snapshot that exists independently of any consciousness, then we shall try conjointly to summon another moment brought as close as possible to the first, and thus have a minimum of time enter into the world without allowing the faintest glimmer of memory to go with it. We shall see that this is impossible. Without an elementary memory that connects the two moments, there will be only one or the other, consequently a single instance, no before or after, no succession, no time. We can bestow upon this memory just what is needed to make the connection; it will be, if we like, this very connection, a mere continuing of the before into the immediate after with a perpetually renewed forgetfulness of what is not the immediately prior moment. We shall nonetheless have introduced memory. To tell the truth, it is impossible to distinguish between the duration, however short it may be, that separates two instants and a memory that connects them, because duration is essentially a continuation of what no longer exists into what does exist. This is real time, perceived and lived. This is also any conceived time, because we cannot conceive a time without imagining it as perceived and lived. Duration therefore implies consciousness; and we place consciousness at the heart of things for the very reason that we credit them with a time that endures.

However, the time that endures is not measurable, whether we think of it as within us or imagine it outside of us. Measurement that is not merely conventional implies, in effect, division and superimposition. But we cannot superimpose successive durations to test whether they are equal or unequal; by hypothesis, the one no longer exists when the other appears; the idea of verifiable equality loses all meaning here. Moreover if real duration becomes divisible, as we shall see, by means of the community that is established between it and the line symbolizing it, it consists in itself of an indivisible and total progress. Listen to a melody with your eyes closed, thinking of it alone, no longer juxtaposing on paper or an imaginary keyboard notes which you thus preserved one for the other, which then agreed to become simultaneous and renounced their fluid continuity in time to congeal in space; you will rediscover, undivided and indivisible, the melody or portion of the melody that you will have replaced within pure duration. Now, our inner duration, considered from the first to the last moment of our conscious life, is something like this melody. Our attention may turn away from it and, consequently, from its indivisibility; but when we try to cut it, it is as if we suddenly passed a blade through a flame — divide only the space it occupied. When we witness a very rapid motion, like that of a shooting star, we quite clearly distinguish its fiery line divisible at will, from the indivisible mobility that it subtends; it is this mobility that is pure duration. Impersonal and universal time, if it exists, is in vain endlessly prolonged from past to future; it is all of a piece; the parts we single out in it are merely those of a space that delineates its track and becomes its equivalent in our eyes; we are dividing the unfolded, not the unfolding. How do we first pass from the unfolding to the unfolded, from pure duration to measurable time? It is easy to reconstruct the mechanism of this operation.

If I draw my finger across a sheet of paper without looking at it, the motion I perform is, perceived from within, a continuity of consciousness, something of my own flow, in a word, duration. If I now open my eyes, I see that my finger is tracing on the sheet of paper a line that is preserved, where all is juxtaposition and no longer succession; this is the unfolded, which is the record of the result of motion, and which will be its symbol as well. Now, this line is divisible, measurable. In dividing and measuring it, I can then say, if it suits me, that I am dividing and measuring the duration of the motion that is tracing it out. It is therefore quite true that time is measured through the intermediary of motion. But it is necessary to add that, if this measurement of time by motion is possible, it is, above all, because we are capable of performing motions ourselves and because these motions then have a dual aspect. As muscular sensation, they are a part of the stream of our conscious life, they endure; as visual perception, they describe a trajectory, they claim a space. I say 'above all' because we could, at a pinch, conceive of a conscious creature reduced to visual perception who would yet succeed in framing the idea of measurable time. Its life would then have to be spent in the contemplation of an outside motion continuing without end. It would also have to be able to extract from the motion perceived in space and sharing the divisibility of its trajectory, the 'pure mobility,' the uninterrupted solidarity of the before and after that is given in consciousness as an indivisible fact. We drew this distinction just before when we were speaking of the fiery path traced out by the shooting star. Such a consciousness would have a continuity of life constituted by the uninterrupted sensation of an external, endlessly unfolding mobility. And the uninterruption of unfolding would still remain distinct from the divisible track left in space, which is still of the unfolded. The latter is divisible and measurable because it is space. The other is duration. Without the continual unfolding, there would be only space, and a space that, no longer subtending a duration, would no longer represent time.

Now, nothing prevents us from assuming that each of us is tracing an uninterrupted motion in space from the beginning to the end of his conscious life. We could be walking day and night. We would thus complete a journey coextensive with our conscious life. Our entire history would then unfold in a measurable time.

Are we thinking of such a journey when we speak of an impersonal time? Not entirely, for we live a social and even cosmic life. Quite naturally we substitute any other person's journey for the one we would make, then any uninterrupted motion that would be contemporaneous with it. I call two flows 'contemporaneous' when they are equally one or two for my consciousness, the latter perceiving them together as a single flowing if it sees fit to engage in an undivided act of attention, and, on the other hand, separating them throughout if it prefers to divide its attention between them, even doing both at one and the same time if it decides to divide its attention and yet not cut it in two. I call two instantaneous perceptions 'simultaneous' that are apprehended in one and the same mental act, the attention here again being able to make one or two out of them at will. This granted, it is easy to see that it is entirely in our interest to take for the 'unfolding of time' a motion independent of that of our own body. In truth, we find it already taken. Society has adopted it for us. It is the earth's rotational motion. But if we accept it, if we understand it as time and not just space, it is because a journey of our own body is always virtual in it, and could have been for us the unfolding of time.

It matters little, moreover, what moving body we adopt as our recorder of time. Once we have exteriorised our own duration as motion in space, the rest follows. Thenceforth, time will seem to us like the unwinding of a thread, that is, like the journey of the mobile entrusted with computing it. We shall say that we have measured the time of this unwinding and, consequently, that of the universal unwinding as well.

But all things would not seem to us to be unwinding along with the thread, each actual moment of the universe would not be for us the tip of the thread, if we did not have the concept of simultaneity at our disposal. We shall soon see the role of this concept in Einstein's theory. For the time being, we would like to make clear its psychological origin, about which we have already said something. The theoreticians of relativity never mention any simultaneity but that of two instants. Anterior to that one, however, is another, the idea of which is more natural: the simultaneity of two flows. We stated that it is of the very essence of our attention to be able to be divided without being split up. When we are seated on the bank of a river, the flowing of the water, the gliding of a boat or the flight of a bird, the ceaseless murmur in our life's deeps are for us three separate things or only one, as we choose. We can interiorise the whole, dealing with a single perception that carries along the three flows, mingled, in its course; or we can leave the first two outside and then divide our attention between the inner and the outer; or, better yet, we can do both at one and the same time, our attention uniting and yet differentiating the three flows, thanks to its singular privilege of being one and several. Such is our primary idea of simultaneity. We therefore call two external flows that occupy the same duration 'simultaneous' because they both depend upon the duration of a like third, our own; this duration is ours only when our consciousness is concerned with us alone, but it becomes equally theirs when our attention embraces the three flows in a single indivisible act.

Now from the simultaneity of two flows, we would never pass to that of two instants, if we remained within pure duration, for every duration is thick; real time has no instants. But we naturally form the idea of instant, as well as of simultaneous instants, as soon as we acquire the habit of converting time into space. For, if a duration has no instants, a line terminates in points. And, as soon as we make a line correspond to a duration, to portions of this line there must correspond 'portions of duration' and to an extremity of the line, an 'extremity of duration'; such is the instant - something that does not exist actually, but virtually. The instant is what would terminate duration if the latter came to a halt. But it does not halt. Real time cannot therefore supply the instant; the latter is born of the mathematical point, that is to say, of space. And yet, without real time, the point would be only a point, not an instant. Instantaneity thus involves two things, a continuity of real time, that is, duration, and a Spatialised time, that is, a line which, described by a motion, has thereby become symbolic of time. This spatialised time, which admits of points, ricochets onto real time and there gives rise to the instant. This would not be possible without the tendency - fertile in illusions which leads us to apply the motion against the distance travelled, to make the trajectory coincide with the journey, and then to decompose the motion over the line as we decompose the line itself; if it has suited us to single out points on the line, these points will then become 'positions' of the moving body (as if the latter, moving, could ever coincide with something at rest, as if it would not thus stop moving at once!). Then, having dotted the path of motion with positions, that is, with the extremities of the subdivisions of the line, we have them correspond to 'instants' of the continuity of the motion - mere virtual stops, purely mental views. We once described the mechanism of this process; we have also shown how the difficulties raised by philosophers over the question of motion vanish as soon as we perceive the relation of the instant to spatialised time, and that of spatialised time to pure duration. Let us confine ourselves here to remarking that no matter how much this operation appears learned, it is native to the human mind; we practice it instinctively. Its recipe is deposited in the language.

Simultaneity of the instant and simultaneity of flow are therefore distinct but complementary things. Without simultaneity of flow, we would not consider these three terms interchangeable: continuity of our inner life, continuity of a voluntary motion which our mind indefinitely prolongs, and continuity of any motion through space. Real duration and spatialised time would not then be equivalent, and consequently time in general would no longer exist for us; there would be only each one's duration. But, on the other hand, this time can be computed thanks only to the simultaneity of the instant. We need this simultaneity of the instant in order (1) to note the simultaneity of a phenomenon with a clock moment, (2) to point off, all along our own duration, the simultaneities of these moments with moments of our duration which are created in the very act of pointing. Of these two acts, the first is the essential one in the measurement of time. But without the second, we would have no particular measurement, we would end up with a figure t representing anything at all, we would not be thinking of time. It is therefore the simultaneity between two instants of two motions outside of us that enables us to measure time; but it is the simultaneity of these moments with moments pricked by them along our inner duration that makes this measurement one of time.

We shall have to dwell upon these two points. But let us first open a parenthesis. We have just distinguished between two 'simultaneities of the instant'; neither of the two is the simultaneity most in question in the theory of relativity, namely, the simultaneity between readings given by two separated clocks. Of that we have spoken in our first chapter; we shall soon be especially occupied with it. But it is clear that the theory of relativity itself cannot help acknowledging the two simultaneities that we have just described; it confines itself to adding a third, one that depends upon a synchronizing of clocks. Now we shall no doubt show how the readings of two separated clocks C and C', synchronized and showing the same time, are or are not simultaneous according to one's point of view. The theory of relativity is correct in so stating; we shall see upon what condition. But it thereby recognizes that an event E occurring beside clock C is given in simultaneity with a reading on clock C in a quite different sense - in the psychologist's sense of the word simultaneity. And likewise for the simultaneity of event E' with the reading on its 'neighbouring' clock C'. For if we did not begin by admitting a simultaneity of this kind, one which is absolute and has nothing to do with the synchronizing of clocks, the clocks would serve no purpose. They would be bits of machinery with which we would amuse ourselves by comparing them with one another; they would not be employed in classifying events; in short, they would exist for their own sake and not to serve us. They would lose their raison d'etre for the theoretician of relativity as for everyone else, for he too calls them in only to designate the time of an event. Now, it is very true that simultaneity thus understood is easily established between moments in two flows only if the flows pass by 'at the same place.' It is also very true that common sense and science itself until now have, a priori, extended this conception of simultaneity to events separated by any distance. They no doubt imagined, as we said further back, a consciousness coextensive with the universe, capable of embracing the two events in a unique and instantaneous perception. But, more than anything else, they applied a principle inherent in every mathematical representation of things and asserting itself in the theory of relativity as well. We find in it the idea that the distinction between 'small' and 'large,' 'not far apart' and 'very far apart,' has no scientific validity and that if we can speak of simultaneity outside of any synchronizing of clocks, independently of any point of view, when dealing with an event and a clock not much distant from one another, we have this same right when the distance is great between the clock and the event or between the two clocks. No physics, no astronomy, no science is possible if we deny the scientist the right to represent the whole universe schematically on a piece of paper. We therefore implicitly grant the possibility of reducing without distorting. We believe that size is not an absolute, that there are only relations among sizes, and that everything would turn out the same in a universe made smaller at will, if the relations among parts were preserved. But in that case how can we prevent our imagination, and even our understanding, from treating the simultaneity of the readings of two very widely separated clocks like the simultaneity of two clocks slightly separated, that is, situated 'at the same place'? A thinking microbe would find an enormous interval between two 'neighbouring' clocks. And it would not concede the existence of an absolute, intuitively perceived simultaneity between their readings. More Einsteinian than Einstein, it would see simultaneity here only if it had been able to note identical readings on two microbial clocks, synchronized by optical signals, which it had substituted for our two 'neighbouring' clocks. Our absolute simultaneity would be its relative simultaneity because it would refer our absolute simultaneity to the readings on its two microbial clocks which it would, in its turn, perceive (which it would, moreover, be equally wrong to perceive) 'at the same place.' But this is of small concern at the moment; we are not criticizing Einstein's conception; we merely wish to show to what we owe the natural extension that has always been made of the idea of simultaneity, after having actually derived it from the ascertainment of two 'neighbouring' events. This analysis, which has until now hardly been attempted, reveals a fact that the theory of relativity could make use of. We see that if our understanding passes here so easily from a short to a long distance, from simultaneity between neighbouring events to simultaneity between widely-separated events, if it extends to the second case the absolute character of the first, it is because it is accustomed to believing that we can arbitrarily modify the dimensions of all things on condition of retaining their relations. But it is time to close the parenthesis. Let us return to the intuitively perceived simultaneity which we first mentioned and the two propositions we had set forth: (1) it is the simultaneity between two instants of two motions outside us that allows us to measure an interval of time; (2) it is the simultaneity of these moments with moments dotted by them along our inner duration that makes this measurement one of time.

The first point is obvious. We saw above how inner duration exteriorises itself as spatialised time and how the latter, space rather than time, is measurable. It is henceforth through the intermediary of space that we shall measure every interval of time. As we shall have divided it into parts corresponding to equal spaces, equal by definition, we shall have at each division point an extremity of the interval, an instant, and we shall regard the interval itself as the unit of time. We shall then be able to consider any motion, any change, occurring beside this model motion; we shall point off the whole length of its unfolding with 'simultaneities of the instant.' As many simultaneities as we shall have established, so many units of time shall we record for the duration of the phenomenon. Measuring time consists therefore in counting simultaneities. All other measuring implies the possibility of directly or indirectly laying the unit of measurement over the object measured. All other measuring therefore bears upon the interval between the extremities even though we are, in fact, confined to counting these extremities. But in dealing with time, we can only count extremities; we merely agree to say that we have measured the interval in this way. If we now observe that science works exclusively with measurements, we become aware that, with respect to time, science counts instants, takes note of simultaneities, but remains without a grip on what happens in the intervals. It may indefinitely increase the number of extremities, indefinitely narrow the intervals; but always the interval escapes it, shows it only its extremities. If every motion in the universe was to accelerate in proportion, including the one that serves as the measure of time, something would change for a consciousness not bound up with intracerebral molecular motions; it would not receive the same enrichment between sunup and sundown; it would therefore detect a change; in fact, the hypothesis of a simultaneous acceleration of every motion in the universe makes sense only if we imagine a spectatorconsciousness whose completely qualitative duration admits of a more or a less without being thereby accessible to measurement. But the change would exist only for that consciousness able to compare the flow of things with that of the inner life. In the view of science nothing would have changed. Let us go further. The speed of unfolding of this external, mathematical time might become infinite; all the past, present, and future states of the universe might be found experienced at a stroke; in place of the unfolding there might be only the unfolded. The motion representative of time would then have become a line; to each of the divisions of this line there would correspond the same portion of the unfolded universe that corresponded to it before in the unfolding universe; nothing would have changed in the eyes of science. Its formulae and calculations would remain what they were.

It is true that exactly at the moment of our passing from the unfolding to the unfolded, it would have been necessary to endow space with an extra dimension. More than thirty years ago, we pointed out that spatialised time is really a fourth dimension of space. Only this fourth dimension allows us to juxtapose what is given as succession: without it, we would have no room. Whether a universe has three, two, or a single dimension, or even none at all and reduces to a point, we can always convert the indefinite succession of all its events into instantaneous or eternal juxtaposition by the sole act of granting it an additional dimension. If it has none, reducing to a point that changes quality indefinitely, we can imagine the rapidity of succession of the qualities becoming infinite and these points of quality being given all at once, provided we bring to this world without dimension a line upon which the points are juxtaposed. If it already had one dimension, if it were linear, two dimensions would be needed to juxtapose the lines of quality - each one indefinite - which were the successive moments of its history. The same observation again if it had two dimensions, if it were a surface universe, an indefinite canvas upon which flat images would indefinitely be drawn, each one covering it completely; the rapidity of succession of these images will again be able to become infinite, and we shall again go over from a universe that unfolds to an unfolded universe, provided that we have been accorded an extra dimension. We shall then have all the endless, piled-up canvases giving us all the successive images that make up the entire history of the universe; we shall possess them all together; but we shall have had to pass from a flat to a volumed universe. It is easy to understand, therefore, why the sole act of attributing an infinite speed to time, of substituting the unfolded for the unfolding, would require us to endow our solid universe with a fourth dimension. Now, for the very reason that science cannot specify the 'speed of unfolding' of time, that it counts simultaneities but necessarily neglects intervals, it deals with a time whose speed of unfolding we may as well assume to be infinite, thereby virtually conferring an additional dimension upon space.

Immanent in our measurement of time, therefore, is the tendency to empty its content into a space of four dimensions in which past, present, and future are juxtaposed or superimposed for all eternity. This tendency simply expresses our inability mathematically to translate time itself, our need to replace it, in order to measure it, by simultaneities which we count. These simultaneities are instantaneities; they do not partake of the nature of real time; they do not endure. They are purely mental views that stake out conscious duration and real motion with virtual stops, using for this purpose the mathematical point that has been carried over from space to time.

But if our science thus attains only to space, it is easy to see why the dimension of space that has come to replace time is still called time. It is because our consciousness is there. It infuses living duration into a time dried up as space. Our mind, interpreting mathematical time, retraces the path it has travelled in obtaining it. From inner duration it had passed to a certain undivided motion which was still closely bound up with it and which had become the model motion, the generator or computer of time; from what there is of pure mobility in this motion, that mobility which is the link between motion and duration, it passed to the trajectory of the motion, which is pure space; dividing the trajectory into equal parts, it passed from the points of division of this trajectory to the corresponding or 'simultaneous' points of division of the trajectory of any other motion. The duration of this last motion was thus measured; we have a definite number of simultaneities; this will be the measure of time; it will henceforth be time itself. But this is time only because we can look back at what we have done. From the simultaneities staking out the continuity of motions, we are always prepared to reascend the motions themselves and, through them, the inner duration that is contemporaneous with them, thus replacing a series of simultaneities of the instant, which we count but which are no longer time, by the simultaneity of flows that leads us back to inner, real duration.

Some will wonder whether it is useful to return to it, and whether science has not, as a matter of fact, corrected a mental imperfection, brushed aside a limitation of our nature, by spreading out 'pure duration' in space. These will say: 'Time, which is pure duration, is always in the course of flowing; we apprehend only its past and its present, which is already past; the future appears closed to our knowledge, precisely because we believe it open to our action - it is the promise or anticipation of unforeseeable novelty. But the operation by which we convert time into space for the purpose of measuring it informs us implicitly of its content. The measurement of a thing is sometimes the revealer of its nature, and precisely at this point mathematical expression turns out to have a magical property: created by us or risen at our bidding, it does more than we asked of it; for we cannot convert into space the time already elapsed without treating all of time the same way. The act by which we usher the past and present into space spreads out the future there without consulting us. To be sure, this future remains concealed from us by a screen; but now we have it there, all complete, given along with the rest. Indeed, what we called the passing of time was only the steady sliding of the screen and the gradually obtained vision of what lay waiting, globally, in eternity. Let us then take this duration for what it is, for a negation, a barrier to seeing all, steadily pushed back; our acts themselves will no longer seem like a contribution of unforeseeable novelty. They will be part of the universal weave of things, given at one stroke. We do not introduce them into the world; it is the world that introduces them ready-made into us, into our consciousness, as we reach them. Yes, it is we who are passing when we say time passes; it is the motion before our eyes which, moment by moment, actualises a complete history given virtually.' Such is the metaphysic immanent in the spatial representation of time. It is inevitable. Clear or confused, it was always the natural metaphysic of the mind speculating upon becoming. We need not discuss it here, still less replace it by another. We have explained elsewhere why we see in duration the very stuff of our existence and of all things, and why, in our eyes, the universe is a continuity of creation. We thus kept as close as possible to the immediate; we asserted nothing that science could not accept and use; only recently, in an admirable book, a philosopher-mathematician affirmed the need to admit of an 'advance of Nature' and linked this conception with ours. For the present, we are confining ourselves to drawing a demarcation line between what is theory, metaphysical construction, and what is purely and simply given in experience; for we wish to keep to experience. Real duration is experienced; we learn that time unfolds and, moreover, we are unable to measure it without converting it into space and without assuming all we know of it to be unfolded. But, it is impossible mentally to spatialize only a part; the act, once begun, by which we unfold the past and thus abolish real succession involves us in a total unfolding of time; inevitably we are then led to blame human imperfection for our ignorance of a future that is present and to consider duration a pure negation, a 'deprivation of eternity.' Inevitably we come back to the Platonic theory. But since this conception must arise because we have no way of limiting our spatial representation of elapsed time to the past, it is possible that the conception is erroneous, and in any case certain that it is purely a mental construction. Let us therefore keep to experience.

If time has a positive reality, if the delay of duration at instantaneity represents a certain hesitation or indetermination inherent in a certain part of things which holds all the rest suspended within it; in short, if there is a creative evolution, I can very well understand how the portion of time already unfolded may appear as juxtaposition in space and no longer as pure succession; I can also conceive how every part of the universe which is mathematically linked to the present and past - that is, the future unfolding of the inorganic world - may be representable in the same schema (we once demonstrated that in astronomical and physical matters prevision is really a vision). We believe that a philosophy in which duration is considered real and even active can quite readily admit Minkowski's and Einstein's space-time (in which, it must be added, the fourth dimension called time is no longer, as in our examples above, a dimension completely similar to the others). On the other hand, you will never derive the idea of a temporal flow from Minkowski's schema. Is it not better, in that case, to confine ourselves, until further notice, to that one of the two points of view which sacrifices nothing of experience, and therefore - not to prejudge the question - nothing of appearances? Besides, how can a physicist wholly reject inner experience if he operates with perceptions and, therefore, with the data of consciousness? It is true that a certain doctrine accepts the testimony of the senses, that is, of consciousness, in order to obtain terms among which to establish relations, then retains only the relations and regards the terms as nonexistent. But this is a metaphysic grafted upon science, it is not science. And, to tell the truth, it is by abstraction that we distinguish both terms and relations: a continual flow from which we simultaneously derive both terms and relations and which is, over and above all that, fluidity; this is the only immediate datum of experience.

But we must close this overly long parenthesis. We believe we have achieved our purpose, which was to describe the salient features of a time in which there really is succession. Abolish these features and there is no longer succession, but juxtaposition. You can say that you are still dealing with time — we are free to give words any meaning we like, as long as we begin by defining that meaning — but we shall know that we are no longer dealing with an experienced time; we shall be before a symbolic and conventional time, an auxiliary magnitude introduced with a view to calculating real magnitudes. It is perhaps for not having first analysed our mental view of the time that flows, our feeling of real duration, that there has been so much trouble in determining the philosophical meaning of Einstein's theories, that is, their relation to reality. Those whom the paradoxical appearance of the theories inconvenienced have declared Einstein's multiple times to be purely mathematical entities. But those who would like to dissolve things into relations, who regard every reality, even ours, as a confusedly perceived mathematics, are apt to declare that Minkowski's and Einstein's space-time is reality itself, that all of Einstein's times are equally real, as much and perhaps more so than the time that flows along with us. We are too hasty in both instances. We have just stated, and we shall soon demonstrate in greater detail, why the theory of relativity cannot express all of reality. But it is impossible for it not to express some. For the time that intervenes in the Michelson-Morley experiment is a real time — real again is the time to which we return with the application of the Lorentz formulae. If we leave real time to end with real time, we have perhaps made use of mathematical artifices in between, but these must have some connection with things. It is therefore a question of allotting shares to the real and to the conventional. Our analyses were simply intended to pave the way for this task.

But we have just uttered the word 'reality'; and in what follows, we shall constantly be speaking of what is real and not real. What shall we mean by that? If it were necessary to define reality in general, to say by what sign we recognize it, we could not do so without classifying ourselves within a school; philosophers are not in agreement, and the problem has received as many solutions as there are shades of realism and idealism. We would, besides, have to distinguish between the standpoints of philosophy and science; the former rather regards the concrete, all charged with quality, as the real; the latter extracts or abstracts a certain aspect of things and retains only size or relation among sizes. Very happily, we have only to be occupied, in all that follows, with a single reality, time. This being so, it will be easy for us to follow the rule we have imposed upon ourselves in the present essay, that of advancing nothing that cannot be accepted by any philosopher or scientist — even nothing that is not implied in all philosophy and science.

Everyone wil surely agree that time is not conceived without a before and an after -- time is succession. Now we have just shown that where there is not some memory, some consciousness, real or virtual, established or imagined, actually present or ideally introduced, there cannot be a before and an after; there is one or the other, not both; and both are needed to constitute time. Hence, in what follows, whenever we shall wish to know whether we are dealing with a real or an imaginary time, we shall merely have to ask ourselves whether the object before us can or cannot be perceived, whether we can or cannot become conscious of it. The case is privileged; it is even unique. If it is a question of colour, for example, consciousness undoubtedly intervenes at the beginning of the study in order to give the physicist the perception of the thing; but the physicist has the right and the duty to substitute for the datum of consciousness something measurable and numerable with which he will henceforward work while granting it the name of the original perception merely for greater convenience. He can do so because, with this original perception eliminated, something remains, or at the very least, is deemed to remain. But what will be left of time if you take succession out of it? And what is left of succession if you remove even the possibility of perceiving a before and an after? I grant you the right to substitute, say, a line for time, since to measure it is quite in order. But a line can be called time only when the juxtaposition it affords is convertible into succession; otherwise you are arbitrarily and conventionally giving that line the name of time. We must be forewarned of this so as not to lay ourselves open to a serious error. What will happen if you introduce into your reasoning and figuring the hypothesis that the thing you called 'time' cannot, on pain of contradiction, be perceived by a consciousness, either real or imaginary? Will you not then be working, by definition, with an imaginary, unreal time? Now such is the case with the times with which we shall often be dealing in the theory of relativity. We shall meet with perceived or perceptible ones - those will be considered real. But there are others that the theory prohibits, as it were, from being perceived or becoming perceptible: if they became so, they would change in scale, so that measurement, correct if it bears upon what we do not perceive, would be false as soon as we do perceive. Why not declare these latter unreal, at least as far as their being 'temporal' goes? I admit that the physicist still finds it convenient to call them time; we shall soon see why. But if we liken these times to the other, we fall into paradoxes that have certainly hurt the theory of relativity, even if they have helped popularise it. It will therefore be no surprise if, in the present study, we require the property of being perceived or perceptible for everything held up as real. We shall not be deciding the question of whether all reality possesses this salient feature. We are only dealing here with the reality of time.