What is an... Accidental?

An accidental in music is a sharp (♯) or flat (♭) sign on a musical score that indicates a temporary change from the given key signature.

The standard musical keyboard – the one you find on pianos, organs and harpsichord – is a design triumph. Essentially, it’s a repeated pattern of seven ascending white notes, marked off by groups of two, then three black notes.

It’s so much easier for the uninitiated to grasp than the complex network of keys on a clarinet or oboe, or that terrifyingly featureless expanse of wood on a violin fingerboard. That’s why children can start picking off tunes, or quasi-tunes, on a piano in minutes.

The standard musical notation reflects the keyboard’s layout: those lines on the stave and the spaces between them represent the white notes. That’s fine if the music you want to play uses only white notes, but most Western music is more complicated.

The Tudor song ‘Greensleeves’ can be played almost entirely on white notes if you start on D. All’s fine till you get to the final phrase: ‘And who but my lady greensleeves.’ The white note, C, on ‘la-a-dy’ sounds wrong. To correct it you have to play the adjacent black note, C sharp, and that's called an Accidental.

.So how do you represent an accidental on paper? In this case you put a little sign, #, before the note. That’s a sharp sign. Suppose you don’t like the white note B on the opening ‘Alas, my lo-o-ove’. Some singers don’t, so they flatten it, in keyboard terms shift down to the neighbouring black note, B flat.

The sign for that is ♭ – and if that looks like a letter ‘b’ to you, that’s because in ancient Gregorian notation the note B was the only one permitted to be raised or lowered in this way.

It got more complicated with the addition of more of those deliciously expressive sharp and flat notes in the Renaissance.

With time, more signs, or ‘accidentals’, were needed: for ‘natural’ indicated that a note which was sharp or flat now isn’t, and then, as the tonal palate enriched, there dawned the strange phenomena of ‘double’ sharps or flats, according to which D is also ‘C double sharp’ or ‘E double flat’. (Too complicated to elaborate here.)

Chopin has a predilection for them, and many a pianist has cursed him for it.

With the arrival of atonal music, the system began to look wobbly: if there isn’t a tonal (key) context, how do you decide whether that black note is an A sharp or a B flat? And what about ‘blue’ intonation in jazz?

But the old notation survived, and today it’s used to codify just about every kind of pitched music known to us. Not bad for a medieval invention.

This article was first published in the June 2016 issue of BBC Music Magazine

Illustration by Adam Howling