  The argument at the end of Book Five is a prelude to the argument and analogies of Sun, Line and Cave in Books Six and Seven. The point of Sun is to contrast the visible and intelligible realms. The former is generated, nurtured and governed by the sun, which also provides the light required by the eye to gain access to the physical world. Corresponding to the sun in the intelligible realm is the Good: “What gives truth to the things known and the power to know to the knower is the Form of the Good. And though it is the cause of knowledge and truth, it is also an object of knowledge.” (508e). Indeed, the Good is responsible for the very ‘being’ of the knowable objects, though Plato never says in what sense the Good is responsible for the knowability and being of the objects of knowledge (see Santas 1980).