The question of the nature of time is as old as philosophy itself. Before philosophy, time was not problematized, it was a pure common-sensical matter. There were various experiences of time, and, accordingly, different words to name it. Whitehead's solution of the temporal conundrum lies in the concept of « creative advance of nature » that is systematically elucidated only in Process and Reality (1929).
To understand the creative advance of nature, one needs to interpret the togetherness of its three aspects - creativity qua concrescence, efficacy qua transition, vision qua initial subjective aim -, and this provides us with the core meaning of time : (i) genuine novelty appears in the World, (ii) past events arc, so to speak, ontologically memorized, and (iii) there is an upward trend in terms of « intensity » of events. These three complementary requirements refresh in their own way the Greek triple understanding of time : time is « aiôn, » lived duration (outside physical time) and destiny, but it is also « chronos, » causal time, and « kairos, » timeliness or the appropriate moment lor action.