In our discussion of first principles, we set down a high degree of unity as one of the distinguishing characteristics of works of art. In this we followed close upon ancient tradition; for the markedly structural character of beauty was noticed by the earliest observers. Plato, the first philosopher of art, identified beauty with simplicity, harmony, and proportion, and Aristotle held the same view. They were so impressed with aesthetic unity that they compared it with the other most highly unified type of thing they knew, the organism; and ever afterwards it has been called "organic unity." With the backing of such authority, unity in variety was long thought to be the same as beauty; and, although this view is obviously one-sided, no one has since succeeded in persuading men that an object can be beautiful without unity. Since art is expression, its unity is, unavoidably, an image of the unity of the things in nature and mind which it expresses. A lyric poem reflects the unity of mood that binds together the thoughts and images of the poet; the drama and novel, the unity of plan and purpose in the acts of men and the fateful sequence of causes and effects in their lives. The statue reflects the organic unity of the body; the painting, the spatial unity of visible things. In beautiful artifacts, the basal unity is the purpose or end embodied in the material structure. But the unity of works of art is not wholly derivative; for it occurs in the free arts like music, where nothing is imitated, and even in the representative arts, as we have observed, it is closer than in the things which are imaged. Aesthetic unity is therefore unique and, if we would understand it, we must seek its reason in the peculiar nature and purpose of art. Since, moreover, art is a complex fact, the explanation of its unity is not simple; the unity itself is very intricate and depends upon many cooperating factors. In the case of the imitative arts, taking the given unity of the objects represented as a basis, the superior unity of the image is partly due to the singleness of the artist's interest. For art, as we know, is never the expression of mere things, but of things so far as they have value. Out of the infinite fullness of nature and of life, the artist selects those elements that have a unique significance for him. Music, when soft voices die, Vibrates in the memory; Odors, when sweet violets sicken, Live within the sense they quicken; Rose leaves, when the rose is dead, Are heaped for the beloved's bed; And so thy thoughts when thou art gone, Love itself shall slumber on.