sion for Natural Philosophy: he thought about it till he was completely puzzled. He could not understand the mechanical and physical causes of the philosophers. He hoped great things from Anaxagoras, who, he was told, said that Mind was the Universal Cause, and who, he expected, would show that everything was ordered in the best way. He was grievously disappointed. Anaxagoras made no use of mind at all, but introduced air, and ether, and a number of strange things as causes. In his disappointment he turned to investigate the question of causation for himself. All his hearers will admit the existence of absolute Ideas. He made up his mind that Ideas are the causes of phenomena, beauty of beautiful things, greatness of great things, and so on. Echecrates interposes the remark that any man of sense will agree to that. Socrates goes on to show that opposite Ideas cannot coexist in the same person: if it is said that Simmias is both tall and short, because he is taller than Socrates and shorter than Phaedo, that is true; but he is only tall and short relatively. An idea must always perish or retreat before its opposite. Further than that, an Idea will not only not admit its opposite; it will not admit that which is inseparable from its opposite. The opposite of cold is heat; and just as cold will not admit heat, so it will not admit fire, which is inseparable from heat. Cold and fire cannot coexist in the same object. So life is the opposite of death, and
