Also if we take two moments of the same family, among the durations which enter into the composition of one moment the smaller durations are completely separated from the smaller durations which enter into the composition of the other moment.

Thus the two moments in their intrinsic properties must exhibit the limits of completely different states of nature.

In this sense the two moments are completely separated.

I will call two moments of the same family 'parallel.' Corresponding to each duration there are two moments of the associated family of moments which are the boundary moments of that duration.

A 'boundary moment' of a duration can be defined in this way.