Relative duration is _the duration through which any movement extends_; that is, the duration through which the “when” of anything in movement glides from _before_ to _after_, and by which the _before_ and the _after_ are linked in mutual relation. Now, the duration through which movement extends is not exactly the duration of the movement itself, but the ground upon which the movement extends its own duration; because movement has nothing actual but a flowing instant, and therefore it has no duration within itself except by reference to an extrinsic ground through which it successively extends. This ground, as we have already shown, is standing duration. And therefore relative duration is nothing else than _standing duration as extrinsically terminated by distinct terms_, or, what amounts to the same terminated by one term which, owing to any kind of movement, acquires distinct and opposite formalities. This conclusion is based on the principle that the foundation of all relations between _before_ and _after_ must be something absolute, having in itself neither _before_ nor _after_, and therefore absolutely standing. This principle is obviously true. The popular notion, on the contrary, that relative duration is the duration of movement, is based on the assumption that movement itself engenders duration--which assumption is false; for we cannot even conceive movement without presupposing the absolute duration upon which the movement has to trace the line of its flowing existence. Thus relative duration is called relative, not because it is itself related, but because it is the ground through which the extrinsic terms are related. It is actively, not passively, relative; it is the _ratio_, not the _rationatum_, the foundation, not the result, of the relativities. In other terms, relative duration is absolute as to its entity, and relative as to the extrinsic denomination derived from the relations of which it is the formal reason. Duration, as absolute, may be styled “the region of all possible _whens_,” just as absolute space is styled “the region of all possible ubications”; and, as relative, it may be styled “the region of all possible succession,” just as relative space is styled “the region of all local movements.” Absolute standing duration and absolute space are the ground of the _here_ and _now_ as statical terms. Relative standing duration and relative space are the ground of the _here_ and _now_ as gliding--that is, as dynamically considered.