There is one other defect in Plato's system which is of capital importance. There runs throughout it a confusion between the notions of reality and existence. To distinguish between existence and reality is an essential feature of all idealism. Even if we go back to the dim idealism of the Eleatics, we shall see this. Zeno, we saw, denied motion, multiplicity, and the world of sense. But he did not deny the existence of the world. That is an impossibility. Even if the world is delusion, the delusion exists. What he denied was the reality of existence. But if reality is not existence, what is it? It is Being, replied the Eleatics. But Being does not exist. Whatever exists is this or that particular sort of being. Being itself is not anywhere to be found. Thus the Eleatics first denied that existence is reality, and then that reality exists. They did not themselves draw this conclusion, but it is involved in their whole position. With a fully developed idealism, like Plato's, this ought to be still clearer. And, in a sense, it is. The individual horse is not real. But it certainly exists. The universal horse is real. But it does not exist. But, upon this last point, Plato wavered and fell. He cannot resist the temptation to think of the absolute reality as existing. And consequently the Ideas are {247} not merely thought as the real universal in the world, but as having a separate existence in a world of their own. Plato must have realised what is, in truth, involved in his whole position, that the absolute reality has no existence. For he tells us that it is the universal, and not any particular individual thing. But everything that exists is an individual thing. Again, he tells us that the Idea is outside time. But whatever exists must exist at some time. Here then this central idealistic thought seems well fixed in Plato's mind. But when he goes on to speak of recollection and reincarnation, when he tells us that the soul before birth dwelt apart in the world of Ideas, to which after death it may hope to return, it is clear that Plato has forgotten his own philosophy, that he is now thinking of the Ideas as individual existences in a world of their own. This is a world of Ideas having a separate existence and place of its own. It is not this world. It is a world beyond. Thus the Platonic philosophy which began on a high level of idealistic thinking, proclaiming the sole reality of the universal, ends by turning the universal itself into nothing but an existent particular. It is the old old story of trying to form mental pictures of that which no picture is adequate to comprehend. Since all pictures are formed out of sensuous materials, and since we can form no picture of anything that is not an individual thing, to form a picture of the universal necessarily means thinking of it as just what it is not, an individual. So Plato commits the greatest sin that can be ascribed to a philosopher. He treats thought as a thing.