If the “when” is considered simply as a termination of standing duration, without regard for anything else, it is called _absolute_, and is defined as _the mode of being of a thing in absolute duration_. This absolute “when” is an _essential mode_ of the contingent being no less than its dependence from the first cause, and is altogether immutable so long as the contingent being exists; for, on the one hand, the contingent being cannot exist but within the domain of divine eternity, and, on the other, it cannot have different modes of being with regard to it, as the standing duration of eternity is all uniform in its infinite virtual extension, and the contingent being, however much we may try to vary its place in duration, must always be in the very middle of eternity. Hence the absolute “when” is altogether unchangeable. If the “when” of a contingent being is compared with that of another contingent being in order to ascertain their mutual relation, then the “when” is called _relative_, and, as such, it may be defined as _the mode of terminating a relation in duration_. This “when” is changeable, not in its intrinsic entity, but in its relative formality; and it is only under this formality that the “when” (_quando_) can be ranked among the predicamental accidents; for this changeable formality is the only thing in it which bears the stamp of an accidental entity. The _before_ and the _after_ of the same contingent being are considered as two distinct relative terms, because the being to which they refer, when existing in the _after_, excludes the _before_; though the absolute “when” of one and the same being is one term only. But of this we shall treat more fully in the sequel. _Seventh question._--“What is relative duration?” Here we meet again the same difficulty which we have encountered in explaining relative space; for in the same manner as relations in space are usually confounded with space itself, so are the intervals in duration confounded with the duration which is the ground of their extension. But, as the reasonings by which we have established the precise notion of relative space can be easily brought to bear on the present subject by the reader himself, we think we must confine ourselves to a brief and clear statement of the conclusions drawn from those reasonings, as applied to duration.