There’s a tendency to associate many of the advances of the 20th-century avant-garde with heavy-duty theory – but it was bare practical necessity that spurred John Cage to develop one of his best-known musical techniques: the prepared piano. Working as a dance accompanist in Seattle in 1940, Cage was asked to prepare a score for a solo dance on an African theme. The available performance space had no pit for the percussion ensemble he had in mind, forcing Cage to make do with a piano tucked to the side. He began manipulating the instrument’s innards with a variety of objects so as to mimic the desired percussive effects – and a eureka moment followed.

Sonatas and Interludes is Cage’s magnum opus for the prepared piano, written between 1946 and 1948. Maro Ajemian, an important new-music advocate of the time, performed the premiere in 1949, which gave Cage’s profile a huge international boost. The score includes meticulous instructions on how to prepare the piano. Bolts, screws, rubber, and plastic are inserted to alter the strings that produce 45 of the 88 notes on the keyboard (only a few of them in the bass). Although the way Cage arrived at his alterations had an improvisatory aspect – he compared his quest for sounds that he liked to “walking along the beach to pick up pretty shells that please you” – these compositions pre-date his introduction of chance processes in music.

In Sonatas and Interludes, Cage explores ideas he had learned from reading art historian Ananda Coomaraswamy on ancient Hindu aesthetic theory about inducing emotions in an audience, centered around a scheme of eight essential emotional states. “The white emotions are the heroic, the erotic, the mirthful, and the wondrous,” says Cage. “The black ones are fear, anger, disgust, and sorrow.” All of these are to be grounded in a ninth “permanent emotion”: tranquility. Cage conceived of the whole work as “a bringing together of these eight emotions, with their tendency toward tranquility.” Their specific presence in each of the pieces comprising the cycle is left up to the listener to determine.

The whole cycle lasts a little over an hour and comprises 16 miniature sonatas, with interludes dividing them into symmetrical subgroups of four. Cage uses the term sonata as a nod to the earlier 18th-century model – as in Scarlatti’s single-movement sonatas – with its simple binary form, in which each half is repeated (AABB); 13 of his 16 sonatas follow this pattern (including the five Joanne Pearce Martin has selected: I, II, IV, V, and XVI, with the third and fourth interludes placed between Sonatas IV and V). Within each piece, Cage lays out a unique, intricate rhythmic structure based on maintaining the same proportions on the small scale as for the whole.

In contrast to his rigid structural plan, Cage’s hybrid piano unpredictably ranges among its varied timbral possibilities, drifting across geographies as well as emotions. Familiar Western sounds mingle with shimmering, dreamlike replicas of an Indonesian gamelan (as in Nos. II and V) or distorted rattlings that suggest electronic music (the third interlude). The muted sound imposed by the preparations overall generates an intimate, meditative atmosphere, one heightened by Cage’s prominent use of silence to shape the music. Even while exaggerating the piano’s identity as a percussion instrument, Cage opens up a novel lyrical dimension – which emerges most clearly as the final (and longest) sonata, No. XVI, at last arrives at a prolonged state of tranquility.

Thomas May writes and lectures about music and theater.