Of the above examples, several are very exalted moral ideas, such as beauty, justice, and goodness. But the case of whiteness will serve to show that the theory attributes reality not only to exalted ideas, but to others also. In fact, we might quite well substitute evil for goodness, and all the same arguments would apply. Or we might take a corporeal object such as the horse, and ask what "horse" means. It does not mean the many individual horses, for since one word is used it must mean one thing, which is related to individual horses, just as whiteness is related to individual white things. It means the universal horse, the idea of the horse in general, and this, just as much as goodness or beauty, must be something objectively real. Now beauty, justice, goodness, whiteness, the horse in general, are all concepts. The idea of beauty is formed by including what is common to all beautiful objects, and excluding those points in which they differ. And this, as we have seen, is just what is meant by a concept. Plato's theory, therefore, is that concepts are objective realities. And he gives to these objective concepts the technical name Ideas. This is his answer to the chief question of philosophy, namely, what, amid all the appearances and unrealities of things, is that absolute and ultimate reality, from which all else is to be explained? It consists, for Plato, in Ideas. Let us see next what the characteristics of the Ideas are. In the first place, they are substances. Substance is a technical term in philosophy, but its philosophical meaning is merely a more consistent development of its {187} popular meaning. In common talk, we generally apply the word substance to material things such as iron, brass, wood, or water. And we say that these substances possess qualities. For example, hardness and shininess are qualities of the substance iron. The qualities cannot exist apart from the substances. They do not exist on their own account, but are dependent on the substance. The shininess cannot exist by itself. There must be a shiny something. But, according to popular ideas, though the qualities are not independent of the substance, the substance is independent of the qualities. The qualities derive their reality from the substance. But the substance has reality in itself. The philosophical use of the term substance is simply a more consistent application of this idea. Substance means, for the philosopher, that which has its whole being in itself, whose reality does not flow into it from anything else, but which is the source of its own reality. It is self-caused, and self-determined. It is the ground of other things, but itself has no ground except itself. For example, if we believe the popular Christian idea that God created the world, but is Himself an ultimate and uncreated being, then, since the world depends for its existence upon God, but God's existence depends only upon Himself, God is a substance and the world is not.