Heraclitus of Ephesus, classed by Ritter among the Ionian philosophers, was born 503 B.C. Like others of his school, he sought a physical ground for all phenomena. The elemental principle he regarded as _fire_, since all things are convertible into it. In one of its modifications this fire, or fluid, self-kindled, permeating everything as the soul or principle of life, is endowed with intelligence and powers of ceaseless activity. "If Anaximenes," says Maurice, not very clearly, "discovered that he had within him a power and principle which ruled over all the acts and functions of his bodily frame, Heraclitus found that there was life within him which he could not call his own, and yet it was, in the very highest sense, _himself_, so that without it he would have been a poor, helpless, isolated creature,--a universal life which connected him with his fellow-men, with the absolute source and original fountain of life.... He proclaimed the absolute vitality of Nature, the endless change of matter, the mutability and perishability of all individual things in contrast with the eternal Being,--the supreme harmony which rules over all." To trace the divine energy of life in all things was the general problem of the philosophy of Heraclitus, and this spirit was akin to the pantheism of the East. But he was one of the greatest speculative intellects that preceded Plato, and of all the physical theorists arrived nearest to spiritual truth. He taught the germs of what was afterward more completely developed. "From his theory of perpetual fluxion," says Archer Butler, "Plato derived the necessity of seeking a stable basis for the universal system in his world of ideas." Heraclitus was, however, an obscure writer, and moreover cynical and arrogant.