Henri Bergson, answered from the texts and cited to the page.
Time, for me, is first and foremost the continuity of inner life itself — not a container in which events occur, but the very flow of experience as it is lived.1 That flow is not a succession of distinct states arranged side by side, as beads on a string; it is a movement in which what came before prolongs itself into what follows, so that the earlier moment is not abolished when the later one arrives but persists within it, keeping the two from being mere snapshots appearing and disappearing in a ceaselessly reborn present.2
A melody heard with closed eyes comes closest to conveying what I mean: it is the very continuity of the melody, the impossibility of breaking it up, that makes the impression of succession upon us — and the moment we cut it into distinct notes, into so many "befores" and "afters," we have imported a spatial image and replaced lived time with something else entirely.3
What we ordinarily call time — the time of clocks, of astronomy, of physics — is precisely that something else. Pure duration, as consciousness perceives it, is not a quantity, and as soon as we attempt to measure it we unwittingly replace it by space.4 The oscillations of the pendulum, the divisions of the dial, these give us a homogeneous medium in which moments are external to one another like bodies in space; they do not give us duration as it actually flows.5
The physicist's time enters formulae as a magnitude; real time, indivisible and qualitative, is what that magnitude abstracts from. There is a metaphysics immanent in the spatial representation of time, and it is worth naming clearly. Once we convert elapsed time into space for the purpose of measuring it, we find ourselves treating all of time the same way — past, present, and future spread out together, the future already there in principle, concealed only by a screen that slides steadily back.6
On that picture, what we called the passing of time is only the gradual revelation of what was given all at once in eternity, and our acts introduce no genuine novelty into the world — they are part of a universal weave already complete. I regard this as the natural metaphysics of a mind speculating upon becoming, and it is inevitable once the spatial substitution has been made.
But it is not the truth of time. Real duration is the very stuff of our existence, and the universe, on my account, is a continuity of creation — which means that the future is genuinely open, not concealed but absent, because it does not yet exist to be revealed.7 Reality, in the end, is mobility itself. There is change, but there are not things which change — the "things" are only artificially taken snapshots of a transition that is all that is naturally experienced.8
there is no doubt but that for us time is at first identical with the continuity of our inner life.Duration and Simultaneity, pp. 90–91
it is a memory within change itself, a memory that prolongs the before into the after, keeping them from being mere snapshots appearing and disappearing in a present ceaselessly reborn.Duration and Simultaneity, pp. 90–91
When we listen to a melody we have the purest impression of succession we could possibly have,--an impression as far removed as possible from that of simultaneity,-and yet it is the very continuity of the melody and the impossibility of breaking it up which make that impression upon us.The Creative Mind, pp. 171–172
Pure duration, that which consciousness perceives, must thus be reckoned among the so-called intensive magnitudes, if intensities can be called magnitudes: strictly speaking, however, it is not a quantity, and as soon as we try to measure it, we unwittingly replace it by space.Time and Free Will, p. 50
Not only do the moments of this duration seem to be external to one another, like bodies in space, but the movement perceived by our senses is the, so to speak, palpable sign of a homogeneous and measurable duration.Time and Free Will, p. 50
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.Duration and Simultaneity, pp. 107–108
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.Duration and Simultaneity, pp. 107–108
reality is mobility itself. That is what I was expressing when I said that there is change, but that there are not things which change.The Creative Mind, pp. 171–172