133. It is impossible to find a primitive measure of motion; we must, at last, take some measure or another, and although arbitrarily chosen, we must refer motion to it. It should be the most uniform measure possible. 134. The resemblance between the ideas of time and space creates a suspicion that they ought to be explained in a similar manner. 135. There is no duration without something which endures; therefore there is no duration separate from things. If nothing existed, there could be no duration. 136. There is no succession without things which succeed: therefore succession cannot be realized as a form independent of things, although it may be conceived in the abstract by itself. 137. Time implies _before_ and _after_, and, consequently, succession. It is succession itself, because in conceiving succession, we conceive time. 138. Succession involves the exclusion of some things by others. This exclusion may either be founded on the essence of things, or be derived from an external cause. 139. Time, therefore, involves exclusion: it is the general idea of the order of changes, or of the mutual relation of being and not-being. 140. If there were no change there would be no time. 141. No time had passed before the existence of the world. There was no other duration than eternity. 142. Eternity is the existence of the infinite being, without any alteration either actual or possible. 143. Time is not any thing absolute and independent of things, but is really in them. It is the order between being and not-being. 144. Co-existence is merely the existence of various beings. To conceive many beings without the idea of the negation of being, is to have the perception of co-existence. 145. Time may be considered under three aspects; the present, the past, and the future. All other relations of time, differently expressed in different idioms, are only combinations of these. 146. The present is the only absolute time: it is conceived without relation to the past or the future; but the past and the future are not conceived without relation to the present. 147. The idea of present accompanies the very idea of being; or rather, it is confounded with the idea of existence; that which has no present existence is not being. 148. The idea of past time is the perception of not-being, or of a being that has been destroyed, in relation to a present being: the idea of future time is the perception of a possible being proceeding from a cause already determined, and in relation to a present being. 149. The idea of time is excited by experience; but it cannot be called a fact of mere observation; for this would be opposed to its intrinsic necessity, by virtue of which it is the object of the exact sciences. 150. Still less can we say, that this idea is confined to the sensible order, since it includes every manner of change in general, whether sensible or supersensible.