The blues as a musical genre is characterized by an ambiguous tonality, constantly oscillating between major and minor¹. In order to render such an ambivalent quality when playing the blues, two distinct (though related) scales are commonly used: the major and the minor blues scales, which quite simply derive from the major and minor pentatonic scales respectively. In each case, a “blue” note is added to the five tones that form the basic major/minor pentatonic sounds. The major and minor blues scales can therefore be considered hexatonic scales, each being comprised of six distinct notes.

From major pentatonic to major blues scale

As presented in this short article, the major pentatonic scale is comprised of scale degrees 1 2 3 5 6. In the key of C for example, that’s C D E G A.

Reflecting the feeling of major-minor ambiguity discussed above, the blue note of choice here is indeed #2 (or, enharmonically, b3): with this addition to the basic tones of the major pentatonic scale, both the augmented second (or, enharmonically, the minor third) and the major third are included in the major blues scale. Note that the blue note creates chromaticism in the scale, dividing the whole-tone interval originally present in the pentatonic between scale degrees 2 and 3 into two semitones. Adhering to widely accepted principles of music notation, we’ll refer to this blue note as #2 in the context of an ascending melody, and as b3 in the context of a descending melody. Hence the formula:

1 2 #2 3 5 6 1 (ascending) / 1 6 5 3 b3 2 1 (descending).

In the key of C, that is:

From minor pentatonic to minor blues scale

The minor pentatonic scale is comprised of scale degrees 1 b3 4 5 b7. In the key of A, that’s A C D E G. As explained in the article already mentioned above, A minor pentatonic and C major pentatonic are relatives. As such, they both feature all the same notes (the only difference being their “starting point” or root: A in the former case, C in the latter).

Quite simply, each minor blues scale also happens to be the relative minor of its major counterpart, hence featuring all the same notes as the latter, but played starting a minor third below its root:

Notice that the blue note is the same tone in both scales: #2/b3 in the context of the major blues scale becomes #4/b5 in the context of the minor blues scale². So the general formula for the minor blues scale is:

1 b3 4 #4 5 b7 1 (ascending) / 1 b7 5 b5 4 b3 1 (descending).

Which scale fits what chord?

As I always tell my students: “in music, there are no hard and fast rules” (Mark Levine actually expressed the idea of musical freedom in jazz using this very wording a few decades ago in his Jazz Piano Book). Pretty much anything goes, as long as you’re honest with what you’re hearing in your mind’s ear. But the notion of infinite possibilities can be daunting… Not to worry though: that’s where the pentatonics and the blues scales step in! They’re a natural, fun, versatile way to begin your journey with improvisation, and will surely prove to be instrumental in developing your inner ear and exploring musical ideas. If you’re wondering over what chords these scales can be played, here’s a very general way of thinking about it to get you started:

• the major pentatonic/blues scale works on dominant (C7, C7(#9)…) and major chords (C6, Cma7) built on the same root as the scale;
• the minor pentatonic/blues scale works on dominant (C7, C7(#9)…) and minor chords (Cmi, Cmi6, Cmi7…) built on the same root as the scale;
• the minor pentatonic/blues scale also works on dominant and minor chords built on a root located a fourth above the tonic of the scale (F7, Fmi7) or a fifth above the tonic of the scale (G7, Gmi7).

This means you can play over a whole blues using just one scale! C minor pentatonic/blues indeed sounds great over C7, F7, and G7 (degrees I, IV, and V of a C blues respectively). Play the scale against each of these chords and listen carefully: you’ll notice the different shades it takes…

Conclusion

That’s all there really is to it! A common misconception is to think that there is only one blues scale. Thinking in terms of having two distinct blues scales (which are, in fact, each other’s relatives) at one’s disposal is indeed a simpler and more fruitful approach.

As I mentioned briefly in this post’s opening paragraph, the added notes (#2/b3 in the case of the major blues scale, and #4/b5 in the case of the minor blues scale) are often called “blue notes.” There is quite some controversy in musicological circles around those so called blue notes… But I tend to agree that the ones mentioned here do indeed largely contribute to giving a bluesy feel to your basic pentatonics, and are indeed the most common. So play around with them, and you’ll see… They sound great!

Notes

¹ In “Blue Note and Blue Tonality,” William Tallmadge writes about “neutral” pitches (quarter-tones), and particularly “neutral” thirds in the context of the blues: singers and instrumentalists traditionally inflect the third in the blues scale, which as a result sounds somewhere in between the tempered minor and major thirds (hence the term “neutral”). On many instruments however (such as the piano), it is impossible to play neutral thirds (you’d have to go in between the keys!). Jazz and blues pianists have no choice but to use either minor or major thirds, or to play around with both.

² For further reading on the topics of pentatonic scales and the blues, I suggest referring to chapters 9 and 10 in Mark’s Jazz Theory Book.

References

Levine, Mark. The Jazz Piano Book. Petaluma: Sher Music Co., 1989.

Levine, Mark. “Chapter Nine: Pentatonic Scales.” In The Jazz Theory Book, 193-218. Petaluma: Sher Music Co., 1995.

Levine, Mark. “Chapter Ten: The Blues.” In The Jazz Theory Book, 219-236. Petaluma: Sher Music Co., 1995.

Tallmadge, William. “Blue Note and Blue Tonality.” The Black Perspective in Music, Autumn 1984 (pp. 155-165).