Jowett: rational principle of the soul

Then we may fairly assume that they are two, and that they differ from one another ; the one with which a man reasons, we may call the rational principle of the soul ; the other, with which he loves, and hungers, and thirsts, and feels the flutterings of any other desire, may be termed the irrational or appetitive, the ally of sundry pleasures and satisfactions ? THE REPUBLIC   BOOK IV