A few words must be said of the sources of our knowledge of pre-Socratic philosophy. If we want to know what Plato and Aristotle thought about any matter, we have only to consult their works. But the works of the earlier philosophers have not come down to us, except in fragments, and several of them never committed their opinions to writing. Our knowledge of their doctrines is the result of the laborious sifting by scholars of such materials as are available. Luckily the material has been plentiful. It may be divided into three classes. First come the fragments of the original writings of the philosophers themselves. These are in many cases long and important, in other cases scanty. Secondly, there are the references in Plato and Aristotle. Of these by far the most important are to be found in the first book of Aristotle's "Metaphysics," which is a history of philosophy up to his own time, and is the first attempt on record to write a history of philosophy. Thirdly, there is an enormous mass of references, some valuable, some worthless, contained in the works of later, but still ancient, writers. {20} CHAPTER II THE IONICS. The earliest Greek philosophers belong to what in after times came to be called the Ionic school. The name was derived from the fact that the three chief representatives of this school, Thales, Anaximander, and Anaximenes, were all men of Ionia, that is to say, the coast of Asia Minor. Thales As the founder of the earliest school in history, Thales of Miletus is generally accounted the founder and father of all philosophy. He was born about 624 B.C. and died about 550 B.C. These dates are approximate, and it should be understood that the same thing is true of nearly all the dates of the early philosophers. Different scholars vary, sometimes as much as ten years, in the dates they give. We shall not enter into these questions at all, because they are of no importance. And throughout these lectures it should be understood that the dates given are approximate. Thales, at any rate, was a contemporary of Solon and Croesus. He was famous in antiquity for his mathematical and astronomical learning, and also for his practical sagacity and wisdom. He is included in {21} all the accounts of the Seven Sages. The story of the Seven Sages is unhistorical, but the fact that the lists of their names differ considerably as given by different writers, whereas the name of Thales appears in all, shows with what veneration he was anciently regarded. An eclipse of the sun occurred in 585 B.C., and Thales is alleged to have predicted it, which was a feat for the astronomy of those times. And he must have been a great engineer, for he caused a diversion of the river Halys, when Croesus and his army were unable to cross it. Nothing else is known of his life, though there were many apocryphal stories.