Ionian School of Philosophy.—The Ionian School includes the earliest Greek philosophers, who lived at Miletus, an Ionian colony in Asia Minor, during the sixth century B.C., and a group of philosophers who lived about one hundred years later and modified the doctrines of their predecessors in several respects. It is usual to distinguish, therefore, the Earlier Ionians and the Later Ionians.
I. Earlier Ionians.—This group includes Thales, Anaximander, and Anaximenes, with whom the history of philosophy in Greece begins. They are called by Aristotle the first “physiologists”, that is, “students of nature”. So far as we know, they confined their philosophical enquiry to the problem of the origin and laws of the physical universe. They taught that the world originated from a primitive substance, which was at once the matter out of which the world was made and the force by which the world was formed. Thales said that this primitive substance was water; Anaximander said that it was “the boundless” (to apeiron); Anaximenes said that it was air, or atmospheric vapor (aer). They agreed in teaching that in this primitive substance there is an inherent force, or vital power. Hence they are said to be Hylozoists and Dynamists. Hylozoism (q.v.) is the doctrine of animated matter, and Dynamism (q.v.) the doctrine that the original cosmothetic force was not distinct from, but identical with, the matter out of which the universe was made. From the scanty materials that have come down to us—a few fragments of the writings of the early Ionians, and allusions in Aristotle‘s writings—it is impossible to determine whether these first philosophers were Theists or Pantheists, although one may perhaps infer from their hylozoistic cosmology that they believed God to be at once the substance and the formative force in the universe.
II. Later Ionians.—This group includes Heraclitus, Empedocles, and Anaxagoras, who lived in the fifth century B.C. These philosophers, like the early Ionians, were deeply interested in the problem of the origin and nature of the universe. But, unlike their predecessors, they distinguished the primitive world-forming force from the primitive matter of which the world was made. In Heraclitus, however, and, to a certain degree, in Empedocles, this mechanism—the doctrine that force is distinct from matter—is expressed hesitatingly and in figurative language. Anaxagoras is the first Greek philosopher to assert definitely and unhesitatingly that the world was formed from a primitive substance by the operation of a force called Intellect. For this reason he is said by Aristotle to be “distinguished from the crowd of random talkers who preceded him” as the “first sober man” among the Greeks. Heraclitus was so impressed with the prevalence of change among physical things that he laid down the principle of panmetabolism: panta rei, “all things are in a constant flux”. Empedocles has the distinction of having introduced into philosophy the doctrine of four elements, or four “roots”, as he calls them, namely fire, air, earth, and water, out of which the centripetal force of love and the centrifugal force of hatred made all things, and are even now making and unmaking all things. Anaxagoras, as has been said, introduced the doctrine of nous, or Intellect. He is blamed however, by Socrates and Plato for having neglected to make the most obvious application of that doctrine to the interpretation of nature as it now is. Having postulated a world-forming Mind, he should, they pointed out, have proceeded to the principle of teleology, that the Mind presiding over natural processes does all things for the best. None of these early philosophers devoted attention to the problems of epistemology and ethics. Socrates was the first to conduct a systematic inquiry into the conditions of human knowledge and the principles of human conduct.