Music and/or literature are the base of the performing arts and of the
large-scale combinations of all the arts, such as opera or motion pictures. The
base, in this context, means that primary art which provides the metaphysical
element and enables the performance to become a concretization of an abstract
view of man.
Without this base, a performance may be entertaining, in such fields as
vaudeville or the circus, but it has nothing to do with art. The performance of
an aerialist, for instance, demands an enormous physical skill—greater,
perhaps, and harder to acquire than the skill demanded of a ballet dancer—but
what it offers is merely an exhibition of that skill, with no further meaning,
i.e., a concrete, not a concretization of anything.