Aristotle, Nicomachean Ethics
H. Rackham, Ed.

But inasmuch as happiness is a certain activity of soul in conformity with perfect virtue, it is necessary to examine the nature of virtue. For this will probably assist us in our investigation of the nature of happiness. [2] Also, the true statesman seems to be one who has made a special study of goodness, since his aim is to make the citizens good and law-abiding men— [3] witness the lawgivers of Crete and Sparta, and the other great legislators of history; [4] but if the study of virtue falls within the province of Political Science, it is clear that in investigating virtue we shall be keeping to the plan which we laid down at the outset. [5]

Now the goodness that we have to consider is clearly human virtue, since the good or happiness which we set out to seek is human good and human happiness. [6] But human virtue means in our view excellence of soul, not excellence of body; also our definition of happiness is an activity of the soul. [7] Now if this is so, clearly it behoves the statesman to have some acquaintance with psychology, just as the physician who is to heal the eye or the other parts of the body¹ must know their anatomy. Indeed a foundation of science is even more requisite for the statesman, inasmuch as politics is a higher and more honorable art than medicine; but physicians of the better class devote much attention to the study of the human body. [8] The student of politics² therefore as well as the psychologist must study the nature of the soul, though he will do so as an aid to politics, and only so far as is requisite for the objects of enquiry that he has in view: to pursue the subject in further detail would doubtless be more laborious than is necessary for his purpose. [9]

Now on the subject of psychology some of the teaching current in extraneous discourses³ is satisfactory, and may be adopted here: namely that the soul consists of two parts, one irrational and the other capable of reason.⁴ [10] （Whether these two parts are really distinct in the sense that the parts of the body or of any other divisible whole are distinct, or whether though distinguishable in thought as two they are inseparable in reality, like the convex and concave sides of a curve, is a question of no importance for the matter in hand.） [11] Of the irrational part of the soul again one division appears to be common to all living things, and of a vegetative nature: I refer to the part that causes nutrition and growth; for we must assume that a vital faculty of this nature exists in all things that assimilate nourishment, 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 unrestrained⁵ 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 mathematics⁶）. 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. [19]

If the other hand it be more correct to speak of the appetitive part of the soul also as rational, in that case it is the rational part which, as well as the whole soul, is divided into two, the one division having rational principle in the proper sense and in itself, the other obedient to it as a child to its father. [20]

Now virtue also is differentiated in correspondence with this division of the soul. Some forms of virtue are called intellectual virtues, others moral virtues: Wisdom or intelligence and Prudence⁷ are intellectual, Liberality and Temperance are moral virtues. When describing a man's moral character we do not say that he is wise or intelligent, but gentle or temperate; but a wise man also is praised for his disposition⁸ , and praiseworthy dispositions we term virtues.