“first cause,” or “first principle.” The achievement of Thales was to dare to assume that the incredible variety and complexity of the natural world nonetheless could be explained by a relatively simple principle. The archē he sought was something like an “ultimate underlying substance,” the basic stuff out of which everything else was composed. As we shall see, Thales’s successors did not accept his theory, and proposed a good number of alternative views of the archē. They did, however, accept and