The career of any great artist can be divided into broad creative periods denned by discernible traits. Olivier Messiaen is no exception, despte the fact that, when discussing his music, it is now part of the common currency to remark upon the constancy with which he stuck to his idiosyncratic musical language. It is true that some of the techniques and spirit which he used in the first of his works to be published, the Préludes, can still be heard in his final masterpiece Éclairs sur I'au-delà…. Indeed, Messiaen himself encouraged this perception, so that the received wisdom is of the composer as a steady accumulator of techniques for a continually expanding style. On one level, therefore, this is a reasonably accurate interpretation in retrospect of Messiaen's career. However, within this broad quality of consistency, it is possible to detect places where the composer markedly changes direction.