IN the last lecture I pointed out that Plato goes beyond Socrates in two ways: in the first place, in so far as he puts opinion--which is his name for the ordinary consciousness before it has been changed by any process of reflexion--between ignorance and knowledge. In other words, he maintains that we are never in a state of pure ignorance from which science has to deliver us. If we ever were in such a state, learning would be impossible, for it would have nothing from which it could start. Opinion, however, is inchoate knowledge; it is a knowledge of appearances, which must indeed be partly illusive, but which cannot be absolutely without relation to the truth. It, therefore, affords a starting-point from which investigation may begin, a material from which, by synthesis and dialectic, truth may be extracted.