Bebop scale is a term referring to common seven-note scales that have an added chromatic passing note. These are frequently used in jazz improvisation and are derived from the modes of the major scale, the melodic minor scale, and the harmonic minor scale. These scales are most often used by David Baker and Barry Harris as a tool to teach jazz improvisation. According to Corey Christiansen, "David Baker, one of the world's finest jazz educators, named these scales the 'bebop scales' because they were used so often by jazz artists from the Bebop Era. These artists include Charlie Christian, Charlie Parker, Lester Young, and Dizzy Gillespie, to name a few." Barry Harris builds these scales from two unrelated 4-note chords, which gives them their names in his system.