Never did ''classical music'' and ''jazz'' come so close as during the 1920's. The first sounds from this period bear witness to the vitality of th epartnership: long before the concepts of ''popular'' and ''serious'' music existed, there had been contacts between the kind of music which demands structured listening, whose laws are those of the ears alone, and the kind which works physically, whose meaning is not exclusively to be found in what can be heard. This polarisation makes itself felt in the twentieth century by virtue fo the fact that European composers begin to take an interest in jazz, a variant form which brought powerful consequences.