The great function of poetry, which we have not yet directly mentioned, is precisely this: to repair to the material of experience, seizing hold of the reality of sensation and fancy beneath the surface of conventional ideas, and then out of that living but indefinite material to build new structures, richer, finer, fitter to the primary tendencies of our nature, truer to the ultimate possibilities of the soul. Our descent into the elements of our being is then justified by our subsequent freer ascent toward its goal; we revert to sense only to find food for reason; we destroy conventions only to construct ideals. Such analysis for the sake of creation is the essence of all great poetry. Science and common sense are themselves in their way poets of no mean order, since they take the material of experience and make out of it a clear, symmetrical, and beautiful world; the very propriety of this art, however, has made it common. Its figures have become mere rhetoric and its metaphors prose. Yet, even as it is, a scientific and mathematical vision has a higher beauty than the irrational poetry of sensation and impulse, which merely tickles the brain, like liquor, and plays upon our random, imaginative lusts. The imagination of a great poet, on the contrary, is as orderly as that of an astronomer, and as large; he has the naturalist's patience, the naturalist's love of detail and eye trained to see fine gradations and essential lines; he knows no hurry; he has no pose, no sense of originality; he finds his effects in his subject, and his subject in his inevitable world. Resembling the naturalist in all this, he differs from him in the balance of his interests; the poet has the concreter mind; his visible world wears all its colours and retains its indwelling passion and life. Instead of studying in experience its calculable elements, he studies its moral values, its beauty, the openings it offers to the soul: and the cosmos he constructs is accordingly an ideal theatre for the spirit in which its noblest potential drama is enacted and its destiny resolved.