. Every event extends over
other events, and every event is extended over by other events. Thus in
the special case of durations which are now the only events directly
under consideration, every duration is part of other durations; and
every duration has other durations which are parts of it. Accordingly
there are no maximum durations and no minimum durations. Thus there is
no atomic structure of durations, and the perfect definition of a
duration, so as to mark out its individuality and distinguish it from
highly analogous durations over which it is passing, or which are
passing over it, is an arbitrary postulate of thought. Sense-awareness
posits durations as factors in nature but does not clearly enable
thought to use it as distinguishing the separate individualities of the
entities of an allied group of slightly differing durations. This is one
instance of the indeterminateness of sense-awareness. Exactness is an
ideal of thought, and is only realised in experience by the selection of
a route of approximation.

The absence of maximum and minimum durations does not exhaust the
properties of nature which make up its continuity. The passage of nature
involves the existence of a family of durations. When two durations
belong to the same family either one contains the other, or they overlap
each other in a subordinate duration without either containing the
other; or they are completely separate. The excluded case is that of
durations overlapping in finite events but not containing a third
duration as a common part.

It is evident that the relation of extension is transitive; namely as
applied to durations, if duration A is part of duration B, and
duration B is part of duration C, then A is part of C. Thus the
first two cases may be combined into one and we can say that two
durations which belong to the same family _either_ are such that there
are durations which are parts of both _or_ are completely separate.

Furthermore the converse of this proposition holds; namely, if two
durations have other durations which are parts of both _or_ if the two
durations are completely separate, then they belong to the same family.

The further characteristics of the continuity of nature--so far as
durations are concerned--which has not yet been formulated arises in
connexion with a family of durations. It can be stated in this way:
There are durations which contain as parts any two durations of the same
family. For example a week c