The hexatonic, or six note, blues scale consists of the minor pentatonic scale plus the 4 or 5 degree. A major feature of the blues scale is the use of blue notes, however, since blue notes are considered alternate 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 and not the individual chord.
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 and blues practice is derived from the "conjunction of 'African scales' and the diatonic western scales. Steven Smith argues that, "to assign blues notes to a 'blues scale' is a momentous mistake, then, after all, unless we alter the meaning of 'scale'.
Despite this, an essentially nine note blues scale is defined by Benward and Saker as a chromatic variation of the major scale featuring a flat third and seventh degrees which, "alternating with the normal third and seventh scale degrees are used to create the blues inflection. These 'blue notes' represent the influence of African scales on this music.