Plato's actual performance of the supreme task of dialectic, the classification and arrangement of all Ideas, is not great. He has made no attempt to complete it. All he has done is to give us numerous examples. And this is, in reality, all that can be expected, for the number of Ideas is obviously infinite, and therefore the task of arranging them cannot be completed. There is, however, one important defect in the dialectic, which Plato ought certainly to have remedied. The supreme Idea, he tells us, is the Good. This, as being the ultimate reality, is the ground of all other Ideas. Plato ought therefore to have derived all other Ideas from it, but this he has not done. He merely asserts, in a more or less dogmatic way, that the Idea of the Good is the highest, but does nothing to connect it with the other Ideas. It is easy to see, however, why he made this assertion. It is, in fact, a necessary logical outcome of his system. For every Idea is perfection in its kind. All the Ideas have perfection in common. And just as the one beauty is the Idea which presides over all beautiful things, so the one perfection must be the supreme Idea which presides {201} over all the perfect Ideas. The supreme Idea, therefore, must be perfection itself, that is to say, the Idea of the Good. On the other hand it might, with equal force, be argued that since all the Ideas are substances, therefore the highest Idea is the Idea of substance. All that can be said is that Plato has left these matters in obscurity, and has merely asserted that the highest Idea is the Good.