By Human Excellence we mean not that of man’s body but that of his soul; for we call Happiness a working of the Soul.
And if this is so, it is plain that some knowledge of the nature of the Soul is necessary for the statesman, just as for the Oculist a knowledge of the whole body, and the more so in proportion as πολιτικὴ is more precious and higher than the healing art: and in fact physicians of the higher class do busy themselves much with the knowledge of the body.
So then the statesman is to consider the nature of the Soul: but he must do so with these objects in view, and so far only as may suffice for the objects of his special inquiry: for to carry his speculations to a greater exactness is perhaps a task more laborious than falls within his province.
In fact, the few statements made on the subject in my popular treatises are quite enough, and accordingly we will adopt them here: as, that the Soul consists of two parts, the Irrational and the Rational (as to whether these are actually divided, as are the parts of the body, and everything that is capable of division; or are only metaphysically speaking two, being by nature inseparable, as are convex and concave circumferences, matters not in respect of our present purpose). And of the Irrational, the one part seems common to other objects, and in fact vegetative; I mean the cause of nourishment and growth (for such a faculty of the Soul one would assume to exist in all things that receive nourishment, even in embryos,1102b and this the same as in the perfect creatures; for this is more likely than that it should be a different one).
Now the Excellence of this manifestly is not peculiar to the human species but common to others: for this part and this faculty is thought to work most in time of sleep, and the good and bad man are least distinguishable while asleep; whence it is a common saying that during one half of life there is no difference between the happy and the wretched;
