The differentiation of M into a geometry of event-particles (instantaneous points) expresses the differentiation of M by its intersections with moments of alien time-systems.

In this way planes and straight lines and event-particles themselves find their being.

Also the parallelism of planes and straight lines arises from the parallelism of the moments of one and the same time-system intersecting M.Similarly the order of parallel planes and of event-particles on straight lines arises from the time-order of these intersecting moments.
The explanation is not given here[13].

It is sufficient now merely to mention the sources from which the whole of geometry receives its physical explanation.
[13] Cf.

_Principles of Natural Knowledge_, and previous chapters of the present work.
The correlation of the various momentary spaces of one time-system is achieved by the relation of cogredience.