What is a... Fugue?

A fugue is music written for several imitative parts which, entering at staggered stages, join together to create a harmonic whole.

Since the Middle Ages, and the first flowering of notated music, composers have striven beyond simple tune-plus-accompaniment.

The result was counterpoint: a texture in which voices interweave like the strands in a cable, or pull against each other like the arc and cord of a fully tensed bow.

The crowning achievement was Fugue. Think of the tune Frère Jacques. If you assemble several voices, and get the singers to stagger their entries, this tune combines with itself to produce satisfying harmonies, yet all the while each voice remains melodic – no musical line is simply subservient to the ‘melody’ on top. This device is called ‘Canon’.

Now imagine that, the First Voice having repeated the phrase ‘Frère Jaques’ and moved on to the higher ‘dormez-vous?’, the Second Voice comes in with the ‘Frère Jacques’ on a different note: say, a fifth higher. In other words, Voice Two starts on the note that ends the phrase ‘dormez-vous?’.

The combination works well enough for a phrase or two, but then the problems begin. You might have to stretch or contract one of the lines to get a satisfactory fit.

And if you want to bring in another voice, singing ‘Frère Jaques’ at the original pitch, you might have to add a few extra notes – a little ‘coda’ – to bring the harmony back to where we started.

Now you have something like the beginning of a fugue. The voices enter one by one, broadly imitating each other, but at alternating pitches: home-note/fifth/home-note… and so on, depending on the number of voices.

The ingenuity comes in the stretching, bending, contracting of ‘Frère Jacques’ (the fugal ‘subject’) and ‘dormez-vous?’ (the ‘countersubject’) to make them fit harmoniously and interestingly with each other in this new harmonic scheme.

Imagine, then, a substantial piece in which the subject, countersubject, plus all the contracted, stretched and bent versions of both, plus the tail-pieces, are combined and recombined, in a regular, carefully contrasted formal scheme, to create a dynamic texture in which each voice is ‘first amongst equals’: each part formed from the same basic material, yet each making its own independent contribution to the musical argument.

This, in basic terms, is Fugue. For the composer it’s perhaps the supreme intellectual challenge. Yet as Bach above all showed, it can also express a staggering variety of moods and characters. For the listener it can be pure joy.

This article was first published in the June 2012 issue of BBC Music Magazine