Modal jazz is a development which began in the later 1950s which takes the mode, or musical scale, as the basis of musical structure and improvisation. Previously, a solo was meant to fit into a given chord progression, but with modal jazz, the soloist creates a melody using one (or a small number of) modes. The emphasis is thus shifted from harmony to melody: "Historically, this caused a seismic shift among jazz musicians, away from thinking vertically (the chord), and towards a more horizontal approach (the scale)," explained pianist Mark Levine.