O body swayed to music, O brightening glance, How can we know the dancer from the dance? William Butler Yeats, Among School Children, 1927 The closing question from Yeats poem Among School Children incites a paradoxical answer. It is possible to observe the particular positions and movements of an individual dancer and thereby identify the performance as a speci?c dance, while it is impossible to observe the performance of the dance devoid of the positions and movements of the dancer. Still, any other dancer may well perform the same dance, and just therefore it is possible to distinguish the...