Bergson's core ideas concern intuition, durée réelle, memory and perception, and the élan vital. In this volume I will mostly be using the terms he used, in French, for durée réelle and élan vital, because the English translations — commonly "duration" or "real time" for durée réelle, and either "vital impetus' or "life drive" (among others) for élan vital, are inadequate.¹ For simplicity I shall attempt to deal with each of them in turn; but as the reader will grasp, they are very closely interrelated, interpenetrating, even built upon each other. The concept of the élan vital will become the most important, to the concerns of this book, as it unfolds, but to understand this concept fully the other concepts must be explored first.