In every history of philosophy for students, the first thing mentioned is that philosophy began with Thales, who said that everything is made of water. Thales was a native of Miletus, in Asia Minor, a flourishing commercial city, in which there was a large slave population, and a bitter class struggle between the rich and poor among the free population. The statement that everything is made of water is to be regarded as a scientific hypothesis, and by no means a foolish one. The Greeks were rash in their hypotheses, but the Milesian school, at least, was prepared to test them empirically. Anaximander, the second philosopher of the Milesian school, is much more interesting than Thales. He held that all things come from a single primal substance, but that it is not water, as Thales held, or any other of the substances that we know. The Milesian school is important, not for what it achieved, but for what it attempted.