The things previously observed are active entities, the 'events.' They are chunks in the life of nature.

These events have to each other relations which in our knowledge differentiate themselves into space-relations and time-relations.

But this differentiation between space and time, though inherent in nature, is comparatively superficial; and space and time are each partial expressions of one fundamental relation between events which is neither spatial nor temporal.

This relation I call 'extension.' The relation of 'extending over' is the relation of 'including,' either in a spatial or in a temporal sense, or in both.

But the mere 'inclusion' is more fundamental than either alternative and does not require any spatio-temporal differentiation.