Let us now return to the great procession of the sages of Hellas. It does not seem necessary to delay long upon Anaxagoras and Empedocles, though both were very great figures in their day. The principle feature in both their systems was that they felt the want of some ideal, or semi-ideal principle to work as a cause in producing the changes in nature. Anaxagoras postulated the original particles to be very diverse in quality and to enter into the composition of ordinary things so as to make up what we call their various qualities. The food we eat, for example, affects all the various parts of human bodies, however different, such as the tissue of the flesh, the hair, the nails, the viscera, because there is in this food, which is made up from corn or other vegetable and animal substances, an assortment of particles each of which contributes to nourish the member or part akin to it. If we ask how external bodies are brought together, and made up into unities, Anaxagoras felt so keenly the necessity of a moving cause that he set up his famous _Nous_, which we cannot translate by the word _mind_, for it was still a material cause, though far more subtle and active than the rest, such as we now imagine ether to be. But even so, Aristotle speaks of Anaxagoras as a great and fruitful innovator, inasmuch as he saw that brute matter cannot begin to act or even to move without some non-material or spiritual, or ideal cause. From what we know of Anaxagoras, he advanced but a little step in this direction himself; he was only groping his way, but to have been pioneer to Plato and to Aristotle is itself no mean praise. In a similar direction, the famous Empedocles postulated the principles of Love and Hate, much as we now postulate Attraction and Repulsion, to explain the varieties, and the movements, in external nature.