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Pentatonic scales: five notes that cannot clash

Take a major scale and remove two notes. What is left is five notes that sound good in any order, in any combination, played by anyone. This is not a beginner's simplification. It is a real property, and half the world's folk music is built on it.

Which two notes leave

The fourth and the seventh. In C major that means F and B go, leaving C, D, E, G, A.

Now play them all at once: . It is not unpleasant. Do the same with the full major scale, , and there is a definite crunch in it.

C major: seven notes, and two of them are the trouble.

C major pentatonic: the fourth and the seventh are gone. Five notes left.

Why removing those two fixes it

F and B are a semitone apart from their neighbours E and C, and they are a tritone apart from each other. Those are the two sources of friction in the scale. Take them out and no two notes left are closer than a whole tone, and the tritone is gone entirely.

So the pentatonic is not five random notes that happen to work. It is the major scale with its two arguments removed. You lose the pull that makes a tune sound like it has arrived somewhere, and you gain a set where nothing can be wrong.

Minor pentatonic is the same five notes

Start the same five on A instead of C and you get A, C, D, E, G. That is minor pentatonic, and it is the scale behind most blues and most rock guitar solos.

Same notes, different home, exactly like the major and minor relationship in key signatures.

The black keys are a pentatonic scale

The five black keys on a piano are F sharp, G sharp, A sharp, C sharp and D sharp. That is a major pentatonic on G flat.

Which is why a child mashing the black keys sounds vaguely oriental and vaguely competent, and why that particular party trick has been used in piano lessons for a century.

What it costs, measured

An instrument can be built pentatonic, and two on this site are. A handpan is tuned once and hammered, and a guzheng has its 21 strings tuned to five repeating notes.

The guzheng reaches from D2 to D6, which is four octaves, the widest range of any instrument here. It can still only play ten of the hundred melodies in our catalogue, and not one of them is refused for being too wide. Every refusal is a tune that wanted a fourth or a seventh.

The handpan is worse off, with 6 pitch letters rather than five, and nineteen of the hundred land on it. Seventy-seven of its refusals fit comfortably inside its range and are turned away for their notes alone. (Its shelf shows nine of the nineteen: the rest were nursery rhymes, and that is a decision rather than a tuning - the repertoire page explains it.)

That is the trade in numbers. You get an instrument a stranger can pick up and not sound bad on, and you give up most of the repertoire written in the last four hundred years in Europe. Whether that is a limitation depends entirely on what you wanted to play.

The full breakdown is on the guzheng repertoire page and the handpan one.