It is impossible, therefore, not to compare works of art one with another. We will concede to the impressionist that anything which anybody finds beautiful is beautiful momentarily; but we must insist on the everyday fact that, because of the operation of the standard as a result of growing experience in art, what once seemed beautiful often ceases to seem so. And we must also insist that among the things surviving as beautiful we inevitably set up a hierarchy, a scale. A plurality of values, each unique and in its own way indispensable to a complete world of values, is not inconsistent with relations of higher and lower among them. The impressionist has taught us to love variety and to renounce the bigotry of the old refusal to accept anything short of the highest. But in aesthetics--and in ethics too, I believe--the standpoint of Spinoza rules: "God is revealed in the mouse as well as in the angel, although less in the mouse than in the angel;" and, I should add, the revelation through the humbler mouse is necessary to a complete revelation of God, that is, of the Good. Or, as Nietzsche said, "_Vieler Edlern naemlich bedarf es, dass es Adel gebe!_" Our appreciation of _Midsummer Night's Dream_ does not prevent us from appreciating _Alice in Wonderland,_ just as our esteem for the man does not hinder our feeling for the peculiar charm of the child. What takes place through the process of comparison is this: we come increasingly to realize what we want of art. Every artist seeks to express something in terms of the material with which he works. But it is only by experimenting with his medium that he learns what he can and what he cannot do; and it is only by constant hospitable, yet discriminating appreciation by us spectators that we, in our turn, discover what to demand of him and commend. Consider, for example, the history of painting. That we want of a picture, sometimes the delineation of emotion and action, yes; but above all and always, the representation of visible nature, with space and atmosphere and light--this purpose has been developed slowly and as the result of many experiments and comparisons. But having won it, we are secure in it. We shall still appreciate the beauty of the primitives and academics, but we shall not be able again to prefer them to the _plein-airistes_. Or recall the development of English poetry. We still admit the contribution of Dryden and Pope, but we shall never have to fight over again the battle won by Wordsworth and his contemporaries for imagination and emotion. Our conception of the purpose of poetry has been enriched by an insight that we cannot permanently lose. There are, to be sure, retrograde movements in the arts--like the Pre-Raphaelite movement in painting--but they are soon recognized as such.