Heraclitus (fl. c.500 B.C.), Greek philosopher. A transition figure between the Milesian philosophers and the later pluralists, Heraclitus stressed unity in the world of change. He follows the Milesians in positing a series of cyclical transformations of basic stuffs of the world; for instance, he holds that fire changes to water and earth in turn. Moreover, he seems to endorse a single source or arche of natural substances, namely fire. But he also observes that natural transformations necessarily involve contraries such as hot and cold, wet and dry. Indeed, without the one contrary the other would not exist, and without contraries the cosmos would not exist. Hence strife is justice, and war is the father and king of all. In the conflict of opposites there is a hidden harmony that sustains the world, symbolized by the tension of a bow or the attunement of a lyre. Scholars disagree about whether Heraclitus’s chief view is that there is a one in the many or that process is reality. Clearly the underlying unity of phenomena is important for him. But he also stresses the transience of physical substances and the importance of processes and qualities. Moreover, his underlying source of unity seems to be a law of process and opposition; thus he seems to affirm both the unity of phenomena and the reality of process. Criticizing his predecessors such as Pythagoras and Xenophanes for doing research without insight, Heraclitus claims that we should listen to the logos, which teaches that all things are one. The logos, a principle of order and knowledge, is common to all, but the many remain ignorant of it, like sleepwalkers unaware of the reality around them. All things come to pass according to the logos; hence it is the law of change, or at least its expression. Heraclitus wrote a single book, perhaps organized into sections on cosmology, politics and ethics, and theology. Apparently, however, he did not provide a continuous argument but a series of epigrammatic remarks meant to reveal the nature of reality through oracular and riddling language. Although he seems to have been a recluse without immediate disciples, he may have stirred Parmenides to his reaction against contraries. In the late fifth century B.C. Cratylus of Athens preached a radical Heraclitean doctrine according to which everything is in flux and there is accordingly no knowledge of the world. This version of Heracliteanism influenced Plato’s view of the sensible world and caused Plato and Aristotle to attribute a radical doctrine of flux to Heraclitus. Democritus imitated Heraclitus’s ethical sayings, and in Hellenistic times the Stoics appealed to him for their basic principles. See also LOGOS, WHITEHEAD. D.W.G.