Heraclitus and Parmenides What is known to us about the pre-Socratic philosopher Heraclitus is obscure, controversial, and of the 140 fragments available, many are of dubious authenticity. And even those which are considered authentic, are open to differing and endless interpretations. But one philosophical thought attributed to Heraclitus is the idea of constant change. His philosophy is summarized as "all things are flowing" (Kirk, 1951, p. 35). What this means is that everything is in constant change. Another quote which aptly characterizes Heraclitus' philosophy is that "War is the father and king of all things" and that war "rests by changing" (ibid). Heraclitus also said that war makes some gods, and some men; it turns some into freemen, and some into slaves. He also says the following about fire: fire dies and changes into air, air dies and changes into water, water dies and becomes earth -- in other words, there is continuous changing of life and death. This should not be called a process, however, as the process suggests that there is one-way movement. For Heraclitus,...

To illustrate this further, Heraclitus explains that there is circular motion in ourselves as well. Some people are alive, others are dead; some are awake, others are asleep; some are old, others are young. Since the ones are changed into the others, this is a circular motion. The same is true of day and night. One succeeds and replaces the other, and vice versa. That is the essence of constant change.
For Parmenides, the most important aspects of his philosophy are rationalization and the austere logic. His main postulate is that "the real is thinkable and that what is unthinkable is nonexistent. When you think, you must always think something; and something means a physical thing" (Boodin, 1943, p. 579). For him the real is rational and logical and what is thinkable must exist. As Parmenides put it in his own words: "It needs must be that what can be spoken and thought is; for it is possible for it to be, and it is not possible for what is nothing to be" (cited in ibid). Thinkable must also be coherent to be…