Music as a whole is richer for the coming of jazz. Although its natural performing habitat is the night-club rather than the concert-hall, the fact that many recordings have endured in the public consciousness over several decades, and that jazz-lovers return to these recordings again and again to find new and life-enhancing things expressed in their sounds, would seem to indicate that jazz is more than just ‘entertainment’, although, like the music of Haydn, agreat deal of it is very entertaining. Jazz has openedup new realms of expression, and is capable of conveying deep feeling in the subtlest shades. It has also made a major contribution to the language of music, in giving us new approaches to melody, harmony and rhythm, and extending the range of tonal colours for both instruments and the voice. Its extensions of instrumental virtuosity have formed one of its most impressive achievements. Some instruments, the saxophone for example, had to wait for the emergence of jazz before their full potential could be realised. But the repertoires of established instruments such as the trumpet and the piano have also been greatly stimulated by their encounter with jazz. The theoretical side of jazz is rich in new concepts, or new ways of looking at traditional things such as harmony and scale-patterns. These techniques, together with the individualistic ethos of the jazz performing tradition, have had a profound influence on the popular music enjoyed by huge numbers of young people. The musical language of pop music, of rock, reggae, soul, and other styles, is steeped in the grammar and structures originally developed by jazz musicians.