His philosophical principle is the direct antithesis of Eleaticism. The Eleatics had taught that only Being is, and Becoming is not at all. All change, all Becoming is mere illusion. For Heracleitus, on the contrary, only Becoming is, and Being, permanence, identity, these are nothing but illusion. All things sublunary are {74} perpetually changing, passing over into new forms and new shapes. Nothing stands, nothing holds fast, nothing remains what it is. "Into the same river," he says, "we go down, and we do not go down; for into the same river no man can enter twice; ever it flows in and flows out." Not only does he deny all absolute permanence, but even a relative permanence of things is declared to be illusory. We all know that everything has its term, that all things arise and pass away, from the insects who live an hour to the "eternal" hills. Yet we commonly attribute to these things at least a relative permanence, a shorter or longer continuance in the same state. But even this Heracleitus will not allow. Nothing is ever the same, nothing remains identical from one consecutive moment to another. The appearance of relative permanence is an illusion, like that which makes us think that a wave passing over the surface of the water remains all the time the same identical wave. Here, as we know, the water of which the wave is composed changes from moment to moment, only the form remaining the same. Precisely so, for Heracleitus, the permanent appearance of things results from the inflow and outflow in them of equivalent quantities of substance. "All is flux." It is not, for example, the same sun which sets to-day and rises to-morrow. It is a new sun. For the fire of the sun burns itself out and is replenished from the vapours of the sea.