 For Brentano the essential feature of a continuum is its inherent capacity to engender boundaries, and the fact that such boundaries can be grasped as coincident. Boundaries themselves possess a quality which Brentano calls plerosis (“fullness”). Plerosis is the measure of the number of directions in which the given boundary actually bounds. Thus, for example, within a temporal continuum the endpoint of a past episode or the starting point of a future one bounds in a single direction, while the point marking the end of one episode and the beginning of another may be said to bound doubly. In the case of a spatial continuum there are numerous additional possibilities: here a boundary may bound in all the directions of which it is capable of bounding, or it may bound in only some of these directions. In the former case, the boundary is said to exist in full plerosis; in the latter, in partial plerosis. Brentano believed that the concept of plerosis enabled sense to be made of the idea that a boundary possesses “parts”, even when the boundary lacks dimensions altogether, as in the case of a point. Thus, while the present or “now” is, according to Brentano, temporally unextended and exists only as a boundary between past and future, it still possesses two “parts” or aspects: it is both the end of the past and the beginning of the future. It is worth mentioning that for Brentano it was not just the “now” that existed only as a boundary; since, like Aristotle he held that “existence” in the strict sense means “existence now”, it necessarily followed that existing things exist only as boundaries of what has existed or of what will exist, or both.