And the reason of this is very obvious. Just as the lower Ideas contain only what is common among the things of a class, and exclude their differences, so the higher Ideas include what is common to the Ideas that come under them, but exclude what is not common. For example, the Idea of colour contains what white, blue, red, and green, have in common. But all colours {245} have not whiteness in common. Green, for example, is not white. Hence the Idea of colour excludes the Idea of whiteness, and it likewise excludes all the Ideas of the other particular colours. So too the highest Idea of all contains only what all the Ideas agree in, but all the rest falls outside it. Thus the Idea of whiteness is perfect in its kind. And as all Ideas are likewise perfect, the highest Idea is that in which they all agree, namely, perfection itself. But this means that the perfection of the Idea of whiteness is contained in the supreme Idea, but its specific character in which it differs from other Ideas is excluded. Its specific character is just its whiteness. Thus the perfection of whiteness is contained in the Good, but its whiteness is not. Consequently it is impossible to deduce whiteness from the Good, because the Good does not contain whiteness. You cannot get out of it what is not in it. When Plato deduced the many from the one, he did so only by showing that the One contains the many. He cannot deduce whiteness from goodness, because goodness does not contain whiteness. The lower Ideas thus have not the character of necessity. They are mere facts. And the hope that we shall find their necessity in the supreme Idea fails. But suppose we waive this. Suppose we grant that there must be an Idea of whiteness, because there is an Idea of the Good. Then why is there an Idea of the Good? What is the necessity of that? We cannot see any necessity in it. What we said of the other Ideas applies with equal force to the highest Idea. The Good may be a necessary Idea, but Plato has not shown it. Thus, though Plato named reason as the Absolute, {246} and though reason is a self-explanatory principle, his account of the detailed content of reason is so unsatisfactory that none of the concepts which he includes in it are really shown to be rational. His philosophy breaks down upon the second test as it did upon the first. He has neither explained the world from the Ideas, nor has he made the Ideas explain themselves.