Abstract
The aim of this paper is to discuss the philosophical premises of Whitehead's definition of time in _The Concept of Nature and other works of the same period. Whitehead probably introduced this definition, which depends on what he calls the "method of extensive abstraction," in 1913, just after the publication of the _Principia Mathematica with Russell. He only published his results in 1919. However, Russell takes up the method, with slight modifications, after personal communication with Whitehead, as soon as 1914, in _Our Knowledge of the External World. It is also carefully studied by G. Mead, in particular in _Philosophy of the Present, and by Merleau-Ponty, in his lectures at the Collège de France. (edited)