There are three major subgenres of bluegrass and one unofficial subgenre. Traditional bluegrass has musicians playing folk songs, tunes with simple traditional chord progressions, and using only acoustic instruments, with an example being Bill Monroe. Progressive bluegrass groups may use electric instruments and import songs from other genres, particularly rock & roll. Examples include Cadillac Sky and Bearfoot. "Bluegrass gospel" has emerged as a third subgenre, which uses Christian lyrics, soulful three- or four-part harmony singing, and sometimes the playing of instrumentals. A newer development in the bluegrass world is Neo-traditional bluegrass; exemplified by bands such as The Grascals and Mountain Heart, bands from this subgenre typically have more than one lead singer. Bluegrass music has attracted a diverse following worldwide. Bluegrass pioneer Bill Monroe characterized the genre as: "Scottish bagpipes and ole-time fiddlin'. It's Methodist and Holiness and Baptist. It's blues and jazz, and it has a high lonesome sound."