Sonatas and Interludes is a collection of twenty pieces for prepared piano by American avant-garde composer John Cage (1912-1992). It was composed in 1946-1948, shortly after Cage's introduction to Indian philosophy and the teachings of art historian Ananda K. Coomaraswamy, both of which became major influences on the composer's later work. Significantly more complex than his other works for prepared piano, Sonatas and Interludes is generally recognized as one of Cage's finest achievements. The cycle consists of sixteen sonatas (thirteen of which are cast in binary form, the remaining three in ternary form) and four more freely structured interludes. The aim of the pieces is to express the eight permanent emotions of the rasa Indian tradition. In Sonatas and Interludes, Cage elevated his technique of rhythmic proportions to a new level of complexity.[2] In each sonata a short sequence of natural numbers and fractions defines the structure of the work and that of it's parts, informing structures as localized as individual melodic lines.