Melody, rhythm and harmony

Jazz music is essentially an interaction between African rhythms and European melodies, though rhythm has assumed a greater significance than melody in the development of jazz. "Swing" is the syncopated rhythm which helps give jazz its distinctive sound. Harmony, which expresses the relationship between various musical notes, has traditionally been the expressive force of European music; in jazz, however, harmony provides part of the framework for improvisation.

Improvisation is at the core of jazz. Yet, while it breaks and redefines musical rules, improvisation doesn't mean "just do whatever you want"; it is always guided by a rhythmic pulse and tonal centre. Freedom is at the heart of improvisation, but in order to ensure some sort of coherence, there must be a basic framework.

Jazz carries a sort of tension between composition and improvisation. One of the earliest jazz musicians, Jelly Roll Morton, combined sensuality and directness with the formal principles of European music - and he showed how the spontaneity of jazz wasn't necessarily tamed by careful preparation. The compositions of Duke Ellington extended the form through unusual key departures and by using the sounds of the different musicians in his band to add texture and colour to his enormous body of work.

Next week: Have the media made sense of the Balkan war?