Resultant relative duration--that is, an interval of flowing duration--admits of the same division into _real_ and _imaginary_. It is real when a real continuous flowing connects the _before_ with the _after_; in all other suppositions it will be imaginary. It may be remarked that the “real continuous flowing” may be either intrinsic or extrinsic. Thus, if God had created nothing but a simple angel, there would have been no other flowing duration than a continuous succession of intellectual operations connecting the _before_ with the _after_ in the angel himself, and thus his duration would have been measured by a series of intrinsic changes. It is evident that in this case one absolute _when_ suffices to extend the interval of duration; for by its gliding from _before_ to _after_ it acquires opposite formalities through which it can be relatively opposed to itself as the subject and the term of the relation. If, on the contrary, we consider the interval of duration between two distinct beings--say Cæsar and Napoleon--then the real continuous flowing by which such an interval is measured is extrinsic to the terms compared; for the _when_ of Cæsar is distinct from, and does not reach, that of Napoleon; which shows that their respective _whens_ have no intrinsic connection, and that the succession comprised between those _whens_ must have consisted of a series of changes extrinsic to the terms compared. It may seem difficult to conceive how an interval of continuous succession can result between two terms of which the one does not attain to the other; for, as a line in space must be drawn by the movement of a single point, so it seems that a length in duration must be extended by the flowing of a single _when_ from _before_ to _after_. The truth is that the interval between the _whens_ of two distinct beings is not obtained by comparing the _when_ of the one with that of the other, but by resorting to the _when_ of some other being which has extended its continuous succession from the one to the other. Thus, when Cæsar died, the earth was revolving on its axis, and it continued to revolve without interruption up to the existence of Napoleon, thus extending the duration of its movement from a _when_ corresponding to Cæsar’s death to a _when_ corresponding to Napoleon’s birth; and this duration, wholly extrinsic to Cæsar and Napoleon, measures the interval between them. As all intervals of duration extend from _before_ to _after_, there can be no interval between co-existent beings, as is evident. In the same manner as two beings whose ubications coincide cannot be distant in space, so two beings whose _whens_ are simultaneous cannot form an interval of duration.