Such very much appears the position of inquirers in the first period of Greek philosophy, which is generally made to extend from its rise under Thales to the time of the Sophists and Socrates. Their thoughts were mainly occupied with the appearances of the physical world: they speculated how it could have arisen. Thus Thales, we are told, imagined its first principle to be water; Anaximander, boundless matter; Anaximenes, air; the Pythagoreans said, all is number; the Eleatic school, all is the one unchangeable being.(328) On the contrary Heracleitus conceived the one Being as ever in motion, involved in perpetual change: in accordance with which he nowhere finds true knowledge, and thinks the mass of men have no understanding for eternal truth.(329) Empedocles of Agrigentum sets forth the four elements, earth, water, air, and fire, as the material principles or roots of things, attaching to these two ideal principles as moving forces, Love as the unitive, and Hatred as the severing.(330) Anaxagoras, over and above mechanical causes, to which he limited himself in the explanation of everything in particular, recognises a divine spirit, which as the finest of all things is simple, unmixed, passionless reason, which came upon chaos, forming and ordering the world out of it.(331) Democritus of Abdera takes for his principles the Full and the Empty, identifying these with Being and Non-being, or Something and Nothing. His Full consists of indivisible atoms.(332) The remarkable thing about all these systems, if we may so call them, is, that while the existing popular religion teemed over, so to say, with the idea of a number of personal agents directing human things, these philosophers nearly all concurred in the attempt to find some one agent, and that material, from which all should spring. As yet even the radical distinction of matter and spirit was not clear to their minds:(333) the soul of the individual man was to them merely a particle of the vital power which disclosed itself through the universe, the purest portion, but a portion still, of primal matter. In their conception of the constituent cause while they advanced towards unity they receded from personality. Even the world-forming Intelligence of Anaxagoras, who first distinctly declares that spirit is not mixed with matter, works only as a power of nature, and is portrayed to us in a semi-sensuous form, as a finer matter.(334)