Anaximenes was the last of the great Milesian philosophers. He was probably a pupil of Anaximander of Miletus and, like Thales before him, he identified one of the tangible elements as the primal substance. For Anaximenes this was air, which by processes of condensation and rarefaction could produce every other kind of matter. He used the rather mystical argument that since air is the breath of life for man it must also be the main principle of the universe.