Chapter 19:

Pentatonic and blues scales

About pentatonic scales

A pentatonic scale is a musical scale with five notes per octave.

Pentatonic scales tend to sound good over many modes and harmonies.

They are often the first scales learned by beginning guitarists. They are easy to play on guitar, in comfortable positions with two notes per string.

Ancient and universal

Pentatonic scales were developed independently by many ancient civilizations.

This may be because the notes of pentatonic scales are acoustically linked by simple pitch ratios. The pentatonic major scale can be constructed by stacking five perfect fifths.

Just intonation vs. equal tempered

Cultures that developed pentatonic modes often used a system of tuning called “just intonation”, in which tones occur naturally as a result of the overtone series. Inconveniently, in just intonation each key contains intervals that are slightly different from the intervals in every other key.

Modern instruments use “equal tempered” tuning instead, in which every key has the exact same intervals. But music composed with just intonation often can’t be reproduced properly on equal tempered instruments. Only instruments like the guitar which support “microtone” intervals (ex. by bending strings) can approximate it.

Major pentatonic and its modes

The major pentatonic scale is the most commonly used pentatonic scale.

As with any scale, modes can be derived from each degree of the major pentatonic.

Modes of the major pentatonic scale contain 3 whole tone intervals (T), and two tone-and-a-half intervals (TS) spaced as far apart as possible.

Just as diatonic modes can be identified by the location of their semitones, pentatonic modes can be identified by the location of their tone-and-a-half intervals.

Of the five modes, the “minor pentatonic” mode is the next most common.

No semitones or tritones

The pentatonic scales used most commonly around the world contain no semitones. Scales without semitones are called “anhemitonic”. They are very consonant and blend well in many contexts.

Pentatonic scales with semitones, called “hemitonic”, are a different and more dissonant beast. Examples include the Japanese “in” or “Sakura” pentatonic scale, and certain interpretations of the blues scale such as the one given later in this chapter.

Pentatonic scales with semitones are less common. In most cases, when people talk about pentatonic scales they are referring to scales without semitones.

Properties of pentatonic intervals

Pentatonic scales without semitones can be played using only the black keys on a piano keyboard.

Comparing the major and minor pentatonic scales to the major and minor diatonic scales, the pentatonic scales have two fewer notes. They omit the two notes that form a tritone together, and which also create semitones with other scale degrees. In the major scale, it’s the 4̂ and 7̂; in the minor scale, it’s the 2̂ and b6̂.

The absence of the two most dissonant intervals in Western music make these pentatonic scales highly consonant.

Major and minor pentatonic

Major pentatonic scale

The major pentatonic scale has tone-and-a-half intervals between degrees 3̂-5̂ and 6̂-1̂.

Just as diatonic scales can be represented by two tetrachords, pentatonic scales can be represented by two “trichords”. The missing fourth and seventh intervals from the diatonic major scale are also shown, to demonstrate how their absence removes the tritone and semitones.

C major pentatonic scale and its trichords on the fretboard

The major pentatonic scale can be played with just the black keys on a piano keyboard, starting from Db.

Minor pentatonic scale

The minor pentatonic scale has tone-and-a-half intervals between degrees 1̂-b3̂ and 5̂-b7̂.

The minor pentatonic scale can be played with just the black keys on a piano keyboard, starting from Bb.

Relative major and minor

Like the natural minor (Aeolian) mode of the major scale, the minor pentatonic mode is a major sixth above, and minor third below, the tonic of the major scale. It’s also the fifth mode of the major pentatonic scale.

C major and relative A minor pentatonic scales on the fretboard

C form

Notice the relative major and minor forms:

• The C major form is the same as the A minor form (below).
• The C minor form is the same as the D major form.

A form

Notice the relative major and minor forms:

• The A major form is the same as the G minor form (below).
• The A minor form is the same as the C major form (above).

G form

Notice the relative major and minor forms:

• The G major form is the same as the E minor form (below).
• The G minor form is the same as the A major form (above).

E form

Notice the relative major and minor forms:

• The E major form is the same as the D minor form (below).
• The E minor form is the same as the G major form (above).

D form

Notice the relative major and minor forms:

• The D major form is the same as the C minor form.
• The D minor form is the same as the E major form (above).

Blues tonality

Origins of the Blues

The Blues originated in the southern United States in the late 19th century, after the American Civil War. It evolved as a combination of traditional African music transmitted by slaves, and the Western European tonality of their enslavers.

Musicologists have long speculated that the Blues sound arises from efforts to reproduce African folk tonalities on Western instruments having twelve-tone equal tempered tuning (12-TET).

Blue notes and flexible pitch areas

When euroclassical music theorists began trying to analyze Blues music, they struggled to understand and even to hear the microtones required to produce Blues intonation on 12-TET Western instruments.

In an effort to simplify Blues tonality for purposes of instruction, the “blues scale” was often described as a minor pentatonic scale with an added b5/#4, or a major pentatonic with a #2/b3. This added tone is often called a “blue note”. But this is an oversimplification, and playing the scale that way does not really sound like the Blues.

A more practical way to view the blues scale is as a series of flexible “pitch areas”, rather than as specific notes.

There are three main pitch areas in the blues:

• Between 2̂ and 3̂ (spanning both major and minor thirds)
• Between 4̂ and 5̂ (or more specifically, 4̂-#4̂ and b5̂-5̂)
• Between 6̂ and b7̂ (or a bit past it)

On guitar, we bend the string within these pitch areas to achieve the desired inflection. Blues musicians treat these pitch areas each as its own distinct “toneme”, a single unit of sound similar to a note, which is then inflected as appropriate based on tonal environment and emotional nuance.

Pentatonic blues scale with pitch areas

Here’s one way to think of a blues scale. Scale degrees are labeled with generic intervals, which actually represent adjustable pitch areas.

For a minor sound, play the lower, minor third range of the 3̂ pitch area.

For a major sound, play the upper, major third range of the 3̂ pitch area.