What is the role of music in dance?
This is a complicated question because music means something different to dance depending on the genre, movement or period that contextualizes the dance. However, to answer the question simply, it might be helpful to look at the differences between classical and postmodern dance. These two dance forms represent two very different ways that music influences dance.
In classical dance forms, such as Indian classical dance and ballet, the music acts as the primary instigator for the dancer's movement. The dance is directly commenting on the music. A complete ballet cannot occur without music, and certain musical styles will suggest certain movement styles. For instance, a score that is somber and adagio will inspire a dance that has similar qualities.
Postmodern dance attacks the assumption that music has to be the primary instigator for dance. Triumphed by choreographers like Merce Cunningham and Trisha Brown, postmodern dance triumphs the use of everyday movement as performance art. Oftentimes the music is a tangential aesthetic choice to the dancer's movement. The two (music and movement) are not necessarily in direct relationship to each other. They may even intentionally clash with one another to create a new meaning. Postmodern dance values parody, irony and hyperreality over a music's intention.
Music is a big part of dance and can make a performance more interesting to watch. Music can change the mood and provide structure in dance. Depending on the type of music, it usually will change the style of dance to suit it, and if the music has a lower tone and is slower, the dance will appear more sad.