SOURCE: G. E. R. Lloyd, "The Problem of Change," in Early Greek Science: Thales to Aristotle, Chatto & Windus, 1970, pp. 36-49.

Lloyd provides a detailed discussion of the philosophical beliefs of Heraclitus. Parmenides, Empedocles, Anaxagoras, Leucippus, and Democritus. He traces the development of philosophical thought among these men, explaining that earlier philosophers assumed that motion and change occurred and that Heraclitus and Parmenides were the first to question this assumption.

The beginnings of an awareness of the problem of change can be traced back to Milesian speculation about the primary substance…. In the early fifth century this became the chief problem in the inquiry concerning nature. The Milesians had taken it for granted that change occurs and that the world of sense-experience is no illusion. But soon afterwards philosophers began to question the basis of our knowledge of the external world. Can we trust the senses, or should we...