The formal elements of poetry are manifold: metrical and strophical patterns, rhyme, rhythm, assonance, alliteration, stress, etc., and forms like the lyric, the drama, the epic. Various as all these factors are, they are to be met with all over the world. The same is true of the motifs of poetry which, however numerous they may be in any language, occur everywhere and at all times. These patterns, forms and motifs are so familiar to us that we take their existence for granted and seldom pause to ask what the common denominator is that makes them so and not otherwise. This denominator, which makes for the astonishing uniformity and limitation of the poetic mode in all periods human society, might perhaps be found in the fact that the creative function we call poetry is rooted in a function even more primordial than culture itself, namely play.