Pentatonics

Five notes. Take a major scale and drop the two that make its semitones, or take a minor triad and add two notes a whole step from their neighbors, and you have the scale that half the world's melodies are made of and that every guitarist learns first: the pentatonic. There are two — major and minor — and they are the same five notes from two different homes. Above is A minor pentatonic on the guitar across the whole neck; the capsule switches to major, the root chip changes the key, the picker the instrument. The figure follows the text from here.

A triad plus two

A minor triad, then the 4 and ♭7 added

The minor pentatonic is a minor triad — 1, ♭3, 5 — with the 4 and the ♭7 added: A C D E G. Look at the wheel and at the neck: the chord tones are three of the five, and the other two sit a whole step from a chord tone on either side, never a semitone. That is the whole secret of why the pentatonic sounds right over its chord — there is no note in it that clashes with a chord tone by a half step. The major pentatonic is the major triad plus the 2 and the 6 — C major pentatonic, C D E G A — built the same way.

The same five from two homes

C major pentatonic turned to A minor pentatonic

C D E G A is C major pentatonic. A C D E G is A minor pentatonic. They are the same five notes; the difference is which one you call home, and the wheel turning is the whole relation — the minor pentatonic starts on the major's fifth note, three semitones down, exactly as the minor scale starts on the major scale's sixth degree. On the instrument switch the two and nothing moves; the numbers change. Every pentatonic shape you learn is therefore two scales, and which one it is depends on the chord under it.

Inside the major scale

The major scale with its 4 and 7 dropped

The major pentatonic is the major scale without its 4 and 7 — the two notes a semitone from a neighbor. So it is inside every major key, three times over: on the I, the IV and the V, the degrees whose chords are major; and the minor pentatonic is inside it three times too, on the ii, the iii and the vi. Chords in a key shows the six on their degrees. A major pentatonic on the key's root — or the minor pentatonic on its relative minor, the same notes — fits every chord in the key at once, which is why it is the first thing anyone plays over a song.

Which pentatonic over which chord

Fitting the key is one thing; fitting the chord of the moment is better. Over a major chord play the major pentatonic on its root; over a minor chord the minor pentatonic on its root. Each is the chord's own three tones plus the two safest neighbors, so every note is either in the chord or a whole step from it. Over a G chord in C major, G major pentatonic — G A B D E, all in the key — instead of C's; over the Am, A minor pentatonic. The notes you leave out change with the chord; the key does not.

The blues scale

Add one note to the minor pentatonic — the ♭5, between the 4 and the 5 — and it is the blues scale, the extra note a passing tone between two that are already there. It is not a sixth degree to rest on; it is a note you go through. The pentatonic underneath is what the ear holds on to.

On the guitar

A minor pentatonic on the guitar falls into five boxes, two notes per string, each sitting on a CAGED shape of the chord — the pentatonic boxes has them one by one, box 1 at the fifth fret being the one every guitarist knows.

On the piano

A minor pentatonic on the piano: white keys with the B and F left out. Every pentatonic on the piano is a five-key pattern; the black keys alone are one — F♯ major pentatonic, or E♭ minor — which is the quickest way to hear what the scale sounds like on its own.

On the ukulele

A minor pentatonic on the ukulele: five notes on four strings, two octaves inside the first twelve frets, the high G string putting the top of the scale under the first finger.

On the bass

A minor pentatonic on the bass: the box shape every bass line lives in, the same on every pair of strings — the root and ♭3 on one string, the 4 and 5 on the next, the ♭7 and the octave on the third.

On the mandolin

A minor pentatonic on the mandolin: three notes on some courses, two on others, the fifths tuning spreading the five across more frets than a guitar's box.

Hearing it

The app plays a pentatonic phrase and you play it back, the root moving each round. Range Shifting on the minor pentatonic is that game here without the mic; a chord loop over pentatonics is the same scale with something to play against.