Jowett: ruling principle

Once more, he said, what ruling principle is there of human things other than the soul, and especially the wise soul ? Do you know of any ? PHAEDO  

"Every one sees that love is a desire, and we know also that non-lovers   desire the beautiful and good. Now in what way is the lover to be distinguished from the non-lover ? Let us note that in every one of us there are two guiding and ruling principles which lead us whither they will ; one is the natural desire of pleasure, the other is an acquired opinion which aspires after the best ; and these two are sometimes in harmony and then again at war, and sometimes the one, sometimes the other conquers. When opinion by the help of reason leads us to the best, the conquering principle is called temperance ; but when desire, which is devoid of reason, rules in us and drags us to pleasure, that power of misrule is called excess. Now excess has many names, and many members, and many forms, and any of these forms when very marked gives a name, neither honourable nor creditable, to the bearer of the name. The desire of eating, for example, which gets the better of the higher reason and the other desires, is called gluttony, and he who is possessed by it is called a glutton — I the tyrannical desire of drink, which inclines the possessor of the desire to drink, has a name which is only too obvious, and there can be as little doubt by what name any other appetite of the same family would be called ; — it will be the name of that which happens to be eluminant. And now I think that you will perceive the drift of my discourse ; but as every spoken word is in a manner plainer than the unspoken, I had better say further that the irrational desire which overcomes the tendency of opinion towards right, and is led away to the enjoyment of beauty, and especially of personal beauty, by the desires which are her own kindred — that supreme desire, I say, which by leading conquers and by the force of passion is reinforced, from this very force, receiving a name, is called love." PHAEDRUS  

And would you not say that he is temperate who has these same elements in friendly harmony, in whom the one ruling principle of reason, and the two subject ones of spirit and desire, are equally agreed that reason ought to rule, and do not rebel ? THE REPUBLIC   BOOK IV

And so we arrive at the result, that the pleasure of the intelligent part of the soul is the pleasantest of the three, and that he of us in whom this is the ruling principle has the pleasantest life. THE REPUBLIC BOOK IX

Now do you suppose that if a person were able to make the original as well as the image, he would seriously devote himself to the image-making branch ? Would he allow imitation to be the ruling principle of his life, as if he had nothing higher in him ? THE REPUBLIC BOOK X