Aristotle, Nicomachean Ethics
H. Rackham, Ed.

including embryos—the same faculty being present also in the fully-developed organism （this is more reasonable than to assume a different nutritive faculty in the latter）. [12] The excellence of this faculty therefore appears to be common to all animate things and not peculiar to man; for it is believed that this faculty or part of the soul is most active during sleep, but when they are asleep you cannot tell a good man from a bad one （whence the saying that for half their lives there is no difference between the happy and the miserable）. [13] This is a natural result of the fact that sleep is a cessation of the soul from the functions on which its goodness or badness depends—except that in some small degree certain of the sense-impressions may reach into soul during sleep, and consequently the dreams of the good are better than those of ordinary men. [14] We need not however pursue this subject further, but may omit from consideration the nutritive part of the soul, since it exhibits no specifically human excellence. [15]

But there also appears to be another element in the soul, which, though irrational, yet in a manner participates in rational principle. In self-restrained and unrestrained¹ people we approve their principle, or the rational part of their souls, because it urges them in the right way and exhorts them to the best course; but their nature seems also to contain another element beside that of rational principle, which combats and resists that principle. [16] Exactly the same thing may take place in the soul as occurs with the body in a case of paralysis: when the patient wills to move his limbs to the right they swerve to the left; and similarly in unrestrained persons their impulses run counter to their principle. But whereas in the body we see the erratic member, in the case of the soul we do not see it; nevertheless it cannot be doubted that in the soul also there is an element beside that of principle, which opposes and runs counter to principle （though in what sense the two are distinct does not concern us here）. [17] But this second element also seems, as we said, to participate in rational principle; at least in the self-restrained man it obeys the behest of principle—and no doubt in the temperate and brave man it is still more amenable, for all parts of his nature are in harmony with principle. [18]

Thus we see that the irrational part, as well as the soul as a whole, is double. One division of it, the vegetative, does not share in rational principle at all; the other, the seat of the appetites and of desire in general, does in a sense participate in principle, as being amenable and obedient to it （in the sense in fact in which we speak of ‘paying heed’ to one's father and friends, not in the sense of the term ‘rational’ in mathematics²）. And that principle can in a manner appeal to the irrational part, is indicated by our practice of admonishing delinquents, and by our employment of rebuke and exhortation generally.