And this it is possible to prove thus: as Aristotle says in the second book On the Soul, to live is to be with the living; and since there are many ways of living--as in the plants to vegetate; in the animals to vegetate and to feel and to move; in men to vegetate, to feel, to move, and to reason, or rather to understand; and since things ought to be denominated by the noblest part, it is evident that in animals to live is to feel--in the brute animals, I say; in man, to live is to use reason.

Wherefore, if to live is the life or existence of man, and if thus to depart from the use of Reason, which is his life, is to depart from life or existence, even thus is that man dead.
And does he not depart from the use of Reason who does not reason or think concerning the aim of his life?
And does he not depart from the use of Reason who does not reason or think concerning the path which he ought to take?
Certainly he does so depart; and this is evident especially in him who has the footprints before him, and looks not at them; and therefore Solomon says in the fifth chapter of Proverbs: "He shall die without instruction; and in the greatness of his folly he shall go astray," that is to say, he is dead who becomes a disciple, and who does not follow his master; and such an one is most vile.
And of him it would be possible for some one to say: How is he dead and yet he walks?
I reply, that as a man he is dead, but as a beast he has remained alive; for as the Philosopher says in the second book On the Soul, the powers of the Soul stand upon itself, as the figure of the quadrangle stands upon the triangle, and the pentagon stands upon the quadrangle; so the sensitive stands upon the vegetative, and the intellectual stands upon the sensitive.

Wherefore, as, by removing the last side of the pentagon, the quadrangle remains, so by removing the last power of the Soul, that is, Reason, the man no longer remains, but a thing with a sensitive soul only, that is, the brute animal.
And this is the meaning or intention of the second part of the devised Song, in which are placed the opinions of others..