The only other objection which may perhaps be made against our conclusions is the following: The foundation of a real relation is that reality through which the terms related communicate with one another. Now, evidently, the _before_ and the _after_, which are the terms of the relation in question, communicate with one another through the same absolute _when_; for they are the same absolute _when_ under two opposite formalities. Hence it follows that the foundation of the relation between _before_ and _after_ is nothing else than the absolute _when_ of a moving being.
To this we answer that the foundation of the relation is not all reality through which the terms related communicate with one another, but only that reality by the common termination of which they become formally related to one another. Hence, since the _before_ and the _after_ do not receive their relative formalities from the absolute _when_, it is idle to pretend that the absolute _when_ is the foundation of the interval of duration. The _before_ and the _after_ communicate with the same absolute _when_ not as a formal, but as a material, cause of their existence--that is, inasmuch as the same _when_ is the subject, not the reason, of both formalities. The only relation to which the absolute _when_ can give a foundation is one of identity with itself in all the extent of its flowing duration. But such a relation presupposes, instead of constituting, an interval in duration. And therefore it is manifest that the absolute _when_ is not the foundation of the relation between _before_ and _after_.
Having thus answered the questions proposed, and given the solution of the few difficulties objected, we must now say a few words about the _division_ and _measurement_ of relative duration, whether fundamental or resultant.
Fundamental or standing duration is divided into _real_ and _imaginary_. This division cannot regard the entity of standing duration, which is unquestionably real, as we have proved. It regards the reality or the unreality of the extrinsic terms conceived as having a relation in duration. The true notion of real, contrasted with imaginary, duration, is the following: Standing duration is called _real_ when it is _really_ relative, viz., when it is extrinsically terminated by real terms between which it founds a real relation; on the contrary, it is called _imaginary_ when the extrinsic terms do not exist in nature, but only in our imagination; for, in such a case, standing duration is not really terminated and does not found real relations, but both the terminations and the relations are simply a figment of our imagination. Thus standing duration, as containing none but imaginary relations, may justly be called “imaginary,” though in an absolute sense it is intrinsically real. Accordingly, the _indefinite_ duration which we imagine when we carry our thought beyond the creation of the world, and which is also called “imaginary,” is not absolute but relative duration, and is not imaginary in itself, but only as to its denomination of relative, because, in the absence of all real terms, there can be none but imaginary relations.