Blues

The note that makes it a blues scale

Take the minor pentatonic and add a single chromatic note a half step below the fifth. That one addition is the whole difference between the two scales, and it is what the name refers to: the blue note. Everything characteristic about the sound follows from it.

It is a dissonance against every chord in a blues, and that is the point of it. Sung rather than played it lands somewhere between the flat fifth and the natural fifth — a pitch a piano cannot produce, and which the voice, a guitar bend and a drawn harmonica note can.

Building it from any root

The formula is fixed, so the scale transposes by counting: root, minor third, fourth, flat fifth, fifth, flat seventh. In C the notes are C E♭ F G♭ G B♭. In E — the key most blues guitar is played in — they are E G A B♭ B D, which is why the shape falls so comfortably into the open position.

Changing the tonic on the circle above redraws the set without changing the pattern. What is worth learning is the relationship between the six degrees, not twelve separate collections of notes.

Placing the blue note

The flat fifth is a passing tone rather than a resting place. Struck on a strong beat and held, it sounds like a wrong note; taken between the fourth and the fifth, going up or coming down, it sounds like the blues. A great deal of the phrasing vocabulary of the idiom rests on that single distinction.

Guitarists usually arrive at it by bending the fourth up a quarter tone instead of fretting it cleanly. Pianists have no bend available and compensate by striking the flat fifth and the natural fifth together or in quick succession — the crushed note that is characteristic of blues piano.

The chords underneath

A twelve-bar blues is three dominant seventh chords — I7, IV7 and V7 — and the same six notes work over all three. That is unusual. In most harmony a scale belongs to a key and is expected to follow the chords; here one scale is held still while the harmony moves beneath it, and the friction between them is the style rather than a fault in it.

It works because each of those chords already carries a note foreign to the major scale of its own root, and the blues scale answers with a flat third and a flat seventh against all three of them. Over the IV7 the flat fifth of the scale becomes the flat ninth of the chord, which is why bar five of a blues so often sounds like the sharpest moment in the form.

On guitar, piano, bass and harmonica

On guitar it is the minor pentatonic box with one extra note per position, which is why it is normally taught second rather than first — the hand already knows the shape. On piano it is easier to hear than to finger: the flat fifth falls on a black key in the common guitar keys and on a white key in C, so the fingering changes character from key to key in a way the guitar shape does not.

On bass it belongs to walking vocabulary more than to soloing, the flat fifth used as a chromatic approach to the fifth. On a diatonic harmonica played in second position the blue notes arrive by bending drawn notes, which is why the instrument sounds idiomatic in this style with no theory behind it at all.

What it is confused with

Three things carry a similar name and are not this scale. The minor pentatonic is this scale without the flat fifth — five notes, no blue note. The major blues scale is a different set, 1 2 b3 3 5 6, built from the major pentatonic and brighter in character. And the scale this catalogue lists as Blues Minor is not a blues scale at all: it is a rotation of the major pentatonic, also called Man Gong, with a flat sixth and no perfect fifth.

The naming here is historical rather than logical, so whenever the word blues turns up in the name of a scale it is worth checking the degrees instead of trusting the label.

Frequently asked questions