Why so many children's songs sit on five notes

Play only the black keys of a piano and you are playing a five-note scale, a pentatonic scale. Tunes from many places use one: Scottish and Irish folk songs, much Chinese, Japanese and Vietnamese folk music, and many West African and Native American songs. "Amazing Grace" and "Auld Lang Syne" fit on the black keys.

Nobody can say for certain why it is so common. Here are the reasons teachers give. A five-note scale leaves out the two notes that sit only a half step from their neighbours, so almost any two notes sound fine together and a child making up a tune rarely hits a harsh clash. And a small child sings most easily in a narrow range, so a song with few notes fits their voice.

Music teachers took this up on purpose. In Hungary, Zoltán Kodály's method starts children on two- and three-note playground songs and builds up to the five. Carl Orff, in Germany, gave children instruments with the clashing bars taken off, so that anything they played would fit.

So a five-note song is less a rule of nature than a very old, very widespread good idea, found again and again.