The key characteristic of classical music that distinguishes it from popular music and folk music is that the repertoire tends to be written down in musical notation , creating a musical part or score . This score typically determines details of rhythm, pitch, and, where two or more musicians (whether singers or instrumentalists) are involved, how the various parts are coordinated. The written quality of the music has enabled a high level of complexity within them: J.S. Bach 's fugues , for instance, ...