No time that can be measured is duration, for heterogeneity is not quantity, not measurable. When we measure a minute we represent a quantity and _ipso facto_ exclude a succession. We represent sixty oscillations of a pendulum, for instance, all together, in one apperception, as we represent sixty points of a line. Now, to represent each of these oscillations in succession, just as it is produced in space, no recollection of a preceding oscillation can enter the representation of any one, for space has kept no trace of it. One is confined to the present, and there is no more succession, or duration, in such a representation than in that of the group as a whole. A third way of representing these oscillations is conceivable. Like the first, it involves retention of preceding oscillations; but, unlike the first, it retains preceding oscillations _in_ succeeding ones, instead of alongside of them; they interpenetrate and interorganize, as was just said, like the notes of a melody. Like the conceptual representation, the intuitional involves a multiplicity. A conceptual multiplicity is distinct, homogeneous, quantitative, numerical; an intuitive multiplicity is indistinct, heterogeneous, qualitative, without analogy with number. Now, it is the latter that characterizes reality; and the multiplicity that we represent conceptually is only a symbol of the reality known to intuition. Oscillations of a pendulum measure nothing; they count simultaneities. Outside of me, in space, there is only a single position of the pendulum; of past positions none remains. Because my duration is an organization and interpenetration of facts, I represent what I call “past” oscillations of the pendulum at the same time that I perceive the actual oscillation. Eliminate the ego, and there is only a single position of the pendulum, and no duration. Eliminate the pendulum, and there is only the heterogeneous duration of the ego. Within the ego is succession without simultaneity or reciprocal externality: without the ego, reciprocal externality without succession, which can exist only for a conscious spectator who remembers the past, and juxtaposits the symbols of the two oscillations in an auxiliary space.