How did music become a more equal partner with choreography in 20th-century ballet?

In the 20th century, music evolved from being a mere servant of the ballet master—providing simple rhythmic support and decoration—to an equal partner with choreography. This shift was driven by the recognition that the highest level of achievement requires music and dance to function as extensions of each other, heard and seen on equal levels of perception.1

Key factors in this transformation include:

• Collaborative Innovation: Impresarios like Serge Diaghilev fostered "total works of art" by bringing together avant-garde composers and choreographers. Notable partnerships, such as that between George Balanchine and Igor Stravinsky, moved beyond mere illustration to a mutual absorption of music and movement.21
• Artistic Independence: Modern choreographers began to reject the idea that music must be "interpreted" or duplicated. Instead, they sought to exploit the relationship between eye and ear, using musical dynamics, harmonic character, and instrumental timbre to change the effect of danced steps.1
• Expanded Scope: The definition of ballet music expanded to include almost every category, from medieval compositions to electronic soundscapes. Some choreographers, like Merce Cunningham, even experimented with independence, choreographing in silence or using music that functioned separately from the dance's structure.13

Ultimately, the ideal became a "perfect analogous concord" where the imagination of the choreographer matches the quality of the music.1