The conception of unity in variety as organic represents an ideal or norm for art, which is only imperfectly realized in many works. There are few novels which would be seriously damaged by the omission of whole chapters, and many a rambling essay in good standing would permit pruning without injury, unless indeed we are made to feel that the apparently dispensable material really contributes something of fullness and exuberance, and so is not superfluous, after all. The unity in some forms of art is tighter than in others; in a play closer than in a novel; in a sonnet more compact than in an epic. In extreme examples, like _The Thousand and One Nights,_ the _Decameron,_ the _Canterbury Tales,_ the unity is almost wholly nominal, and the work is really a collection, not a whole. With all admissions, it remains true, however, that offenses against the principle of unity in variety diminish the aesthetic value of a work. These offenses are of two kinds--the inclusion of the genuinely irrelevant, and multiple unity, like double composition in a picture, or ambiguity of style in a building. There may be two or more parallel lines of action in a play or a novel, two or more themes in music, but they must be interwoven and interdependent. Otherwise there occurs the phenomenon aptly called by Lipps "aesthetic rivalry"--each part claims to be the whole and to exclude its neighbor; yet being unable to do this, suffers injury through divided attention. Unity in variety may exist in any one or more of three modes--the harmony or union of cooperating elements; the balance of contrasting or conflicting elements; the development or evolution of a process towards an end or climax. The first two are predominantly static or spatial; the last, dynamic and temporal. I know of no better way of indicating the characteristic quality of each than by citing examples.