You’ve heard it talked about and you’ve experienced it from a variety of musicians, but do you really know what a blues scale is? Here’s what you need to know.
There’s no clear-cut definition what is or is not a blues scale other than one can be used to create the wide variety of music known as blues. However, most musicians agree that the six-note blues scale is the starting point. This blues scale consists of the five-note minor pentatonic scale plus one note often referred to as (surprise) the blue note. Since Western music recognizes 12 minor keys, one for each note in an octave, so you can create 12 of these six-note blues scales using this method, one for each key.
The minor pentatonic scale consists of five notes carved out of the seven-note natural minor scale (yes, there is more than one minor scale). Specifically, they are the scale tones 1, 3, 4, 5, and 7 of any natural minor scale (1 being the root note of the scale, i.e. the note that names the scale). The additional note, the blue note, that turns this minor pentatonic scale into the blues scale is the flatted 5th tone of the natural minor scale. So, in order, the blues scale is made up of the natural minor scale tones 1, 3, 4, 5-flat, 5, and 7. For reasons beyond the scope of this topic, you can also create the same blues scale from the corresponding major scale by playing tones 1, 3-flat, 4, 5-flat, 5, and 7-flat of said major scale.
These are the notes. How you play them is the stuff of legends.
It’s worth noting that the so-called blue note is an interval from the root known as a tritone (abbreviated TT), which is an interval of three full tones. The tritone has a particularly dissonant, unstable sound that lends itself nicely to blues music. Try it yourself on a piano keyboard: in the key of F play root F and tritone B alternatively and listen for the dissonance. In medieval western music, this sinister interval was avoided, or used for effect, and often referred to as diabolus in musica (“the Devil in music”). In modern times, this sonic uneasiness has been a staple of heavy metal music as well as blues.
Another variation of a blues scales is the major pentatonic (1, 2, 3, 5, 6 of the major scale) plus the flatted third. In this case, the flatted third is what gives the bluesy sound. Remember that the flatted third is one of main differences between a major chord (having a natural third) and a minor chord (having the flatted third), so alternating between them creates a bluesy feeling.
But don’t try to put blues in a box, it won’t stay there. Blues is more about how you play the notes, less about what notes you play.