Doubtless there is in every art an element of mere knowledge or science, and that element is progressive. But there is another element, too, which does not depend on knowledge and which does not progress but has a kind of stationary and eternal value, like the beauty of the dawn, or the love of a mother for her child, or the joy of a young animal in being alive, or the courage of a martyr facing torment. We cannot for all our progress get beyond these things; there they stand, like light upon the mountains. The only question is whether we can rise to them. And it is the same with all the greatest births of human imagination. As far as we can speculate, there is not the faintest probability of any poet ever setting to work on, let us say, the essential effect aimed at by Aeschylus in the Cassandra-scene of the _Agamemnon_, and doing it better than Aeschylus. The only thing which the human race has to do with that scene is to understand it and get out of it all the joy and emotion and wonder that it contains. This eternal quality is perhaps clearest in poetry: in poetry the mixture of knowledge matters less. In art there is a constant development of tools and media and technical processes. The modern artist can feel that, though he cannot, perhaps, make as good a statue as Pheidias, he could here and there have taught Pheidias something: and at any rate he can try his art on subjects far more varied and more stimulating to his imagination. In philosophy the mixture is more subtle and more profound. Philosophy always depends in some sense upon science, yet the best philosophy seems generally to have in it some eternal quality of creative imagination. Plato wrote a dialogue about the constitution of the world, the _Timaeus_, which was highly influential in later Greece, but seems to us, with our vastly superior scientific knowledge, almost nonsensical. Yet when Plato writes about the theory of knowledge or the ultimate meaning of Justice or of Love, no good philosopher can afford to leave him aside: the chief question is whether we can rise to the height and subtlety of his thought.