owledge by
sense-awareness is a duration. Accordingly we have now to explain how
moments are derived from durations, and also to explain the purpose
served by their introduction.

A moment is a limit to which we approach as we confine attention to
durations of minimum extension. Natural relations among the ingredients
of a duration gain in complexity as we consider durations of increasing
temporal extension. Accordingly there is an approach to ideal simplicity
as we approach an ideal diminution of extension.

The word 'limit' has a precise signification in the logic of number and
even in the logic of non-numerical one-dimensional series. As used here
it is so far a mere metaphor, and it is necessary to explain directly
the concept which it is meant to indicate.

Durations can have the two-termed relational property of extending one
over the other. Thus the duration which is all nature during a certain
minute extends over the duration which is all nature during the
30th second of that minute. This relation of 'extending
over'--'extension' as I shall call it--is a fundamental natural relation
whose field comprises more than durations. It is a relation which two
limited events can have to each other. Furthermore as holding between
durations the relation appears to refer to the purely temporal
extension. I shall however maintain that the same relation of extension
lies at the base both of temporal and spatial extension. This discussion
can be postponed; and for the present we are simply concerned with the
relation of extension as it occurs in its temporal aspect for the
limited field of durations.

The concept of extension exhibits in thought one side of the ultimate
passage of nature. This relation holds because of the special character
which passage assumes in nature; it is the relation which in the case of
durations expresses the properties of 'passing over.' Thus the duration
which was one definite minute passed over the duration which was its
30th second. The duration of the 30th second was part of the duration of
the minute. I shall use the terms 'whole' and 'part' exclusively in this
sense, that the 'part' is an event which is extended over by the other
event which is the 'whole.' Thus in my nomenclature 'whole' and 'part'
refer exclusively to this fundamental relation of extension; and
accordingly in this technical usage only events can be either wholes or
parts.

The continuity of nature arises from extension