  Although his words are meant to provide concrete vicarious encounters with the world, Heraclitus adheres to some abstract principles which govern the world. Already in antiquity he was famous for advocating the coincidence of opposites, the flux doctrine, and his view that fire is the source and nature of all things. In commenting on Heraclitus, Plato provided an early reading, followed tentatively by Aristotle, and popular down to the present (sharpened and forcefully advocated by Barnes 1982, ch. 4). According to Barnes’ version, Heraclitus is a material monist who believes that all things are modifications of fire. Everything is in flux (in the sense that “everything is always flowing in some respects,” 69), which entails the coincidence of opposites (interpreted as the view that “every pair of contraries is somewhere coinstantiated; and every object coinstantiates at least one pair of contraries,” 70). The coincidence of opposites, thus interpreted, entails contradictions, which Heraclitus cannot avoid. On this view Heraclitus is influenced by the prior theory of material monism and by empirical observations that tend to support flux and the coincidence of opposites. In a time before the development of logic, Barnes concludes, Heraclitus violates the principles of logic and makes knowledge impossible.