A major feature of the blues scale is the use of blue notes; however, since blue notes are considered alternative inflections, a blues scale may be considered to not fit the traditional definition of a scale. At its most basic, a single version of this blues scale is commonly used over all changes (or chords) in a twelve bar blues progression. Likewise, in contemporary jazz theory, its use is commonly based upon the key rather than the individual chord. The evolution of this scale may be traced back to Asia (pentatonic major) through native North America (pentatonic minor) with the addition of the flat 5 blue note (slave trade/Africa).
The heptatonic, or seven-note, conception of the blues scale is as a diatonic scale (a major scale) with lowered third, fifth, and seventh degrees Blues practice is derived from the "conjunction of 'African scales' and the diatonic western scales".