Poulenc said that he was not inventive in his harmonic language. The composer Lennox Berkeley wrote of him, "All through his life, he was content to use conventional harmony, but his use of it was so individual, so immediately recognizable as his own, that it gave his music freshness and validity." Keck considers Poulenc's harmonic language "as beautiful, interesting and personal as his melodic writing ... clear, simple harmonies moving in obviously defined tonal areas with chromaticism that is rarely more than passing". Poulenc had no time for musical theories; in one of his many radio interviews he called for "a truce to composing by theory, doctrine, rule!" He was dismissive of what he saw as the dogmatism of latter-day adherents to dodecaphony, led by René Leibowitz, and greatly regretted that the adoption of a theoretical approach had affected the music of Olivier Messiaen, of whom he had earlier had high hopes. To Hell, almost all Poulenc's music is "directly or indirectly inspired by the purely melodic associations of the human voice". Poulenc was a painstaking craftsman, though a myth grew up – ""la légende de facilité"" – that his music came easily to him; he commented, "The myth is excusable, since I do everything to conceal my efforts."