Jazz harmony began to differentiate from classical harmony in the early 20th century. Jazz music emerged from African American communities in New Orleans, Louisiana, and drew influences from blues, ragtime, and brass band music. Jazz harmony is characterized by its use of extended chords, such as the dominant seventh and ninth chords, and its emphasis on improvisation.
One of the primary reasons for the divergence of jazz and classical harmony is the difference in their respective approaches to melody and harmony. Classical music emphasizes the horizontal aspect of melody, which is the way the notes of a melody are arranged over time. In contrast, jazz places greater emphasis on the vertical aspect of harmony, which is the way the notes of a chord are arranged vertically.
Another reason for the differentiation of jazz and classical harmony is the influence of African American musical traditions. Jazz music was influenced by African American music, which emphasizes rhythmic complexity, syncopation, and call-and-response patterns. These elements are not present in classical music, which is based on European musical traditions.
Furthermore, jazz musicians began to experiment with new harmonic structures, such as modal jazz, which used modes instead of traditional chord progressions. Modal jazz is characterized by a more static harmony that allows for greater freedom in improvisation. This departure from traditional chord progressions was not present in classical music, which relied on functional harmony and chord progressions.
Jazz harmony also reflects the influence of other musical traditions, such as Latin American music and the blues. Latin American music introduced new rhythms and harmonic structures to jazz music, while the blues provided a foundation for jazz harmony with its emphasis on the use of dominant seventh chords and blue notes.
In conclusion, jazz harmony began to differentiate from classical harmony due to several factors, including the emphasis on the vertical aspect of harmony, the influence of African American musical traditions, the experimentation with new harmonic structures, and the influence of other musical traditions. Jazz harmony is characterized by its use of extended chords, its emphasis on improvisation, and its departure from traditional chord progressions.