For example we conceive of the distribution of matter in space at an instant.

This is a very useful concept in science especially in applied mathematics; but it is a very complex idea so far as concerns its connexions with the immediate facts of sense-awareness.

There is no such thing as nature at an instant posited by sense-awareness.

What sense-awareness delivers over for knowledge is nature through a period.

Accordingly nature at an instant, since it is not itself a natural entity, must be defined in terms of genuine natural entities.