A broader definition that encompasses different eras of jazz has been proposed by Travis Jackson: "it is music that includes qualities such as swing, improvising, group interaction, developing an 'individual voice', and being open to different musical possibilities". Krin Gibbard argued that "jazz is a construct" which designates "a number of musics with enough in common to be understood as part of a coherent tradition". In contrast to commentators who have argued for excluding types of jazz, musicians are sometimes reluctant to define the music they play. Duke Ellington, one of jazz's most famous figures, said, "It's all music."