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[REF] and blues practice is derived from the "conjunction of 'African scales' and the diatonic western scales" [REF].
A different and "non-formal" way of playing the scale is possible by use of "quarter step", added to 3rd and 7th degree of minor blues scale.