Poulenc's music is essentially diatonic. In Henri Hell's view, this is because the main feature of Poulenc's musical art is his melodic gift. In the words of Roger Nichols in the "Grove" dictionary, "For the most important element of all was melody and he found his way to a vast treasury of undiscovered tunes within an area that had, according to the most up-to-date musical maps, been surveyed, worked and exhausted." The commentator George Keck writes, "His melodies are simple, pleasing, easily remembered, and most often emotionally expressive."