It is my purpose to speak of that virtue which is called moral and reputed to be so, which differs from contemplative virtue chiefly in that it has as its material the emotions of the soul and as its form reason, and to inquire what its essential nature is and how, by its nature, it subsists; whether, also, that part of the soul which receives it is equipped with its own reason, or does but share in the reason of some other part; and if the latter, whether it does this after the manner of elements that are mingled with what is better than themselves, or rather, whether this portion of the soul is guided and governed by another part and in this sense may be said to share in that governing part’s power. For that it is possible for virtue also to have come into being and to remain entirely independent of matter and free from all admixture with it, I think is quite obvious. It is better, however, to run summarily through the opinions of the philosophers holding opposing views, not so much for the sake of inquiring into them as that my own opinions may become clearer and more firmly established when those of the philosophers in question have been presented.