Aristotle, Nicomachean Ethics
H. Rackham, Ed.

that happiness is a thing honored and perfect. [8] This seems to be borne out by the fact that it is a first principle or starting-point, since all other things that all men do are done for its sake; and that which is the first principle and cause of things good we agree to be something honorable and divine.13.

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,