The Six Paradoxes of Communism:

1. Everyone has a job, but no one actually does any work.
2. No one actually does any work, but production targets are always reached.
3. Production targets are always reached, but the shops are always empty.
4. The shops are always empty, but everyone has all they need.
5. Everyone has all they need, but no one is happy.
6. No one is happy, but they always vote the Communists back in.

(Russian joke)

"How can music be funny?" a bemused friend once asked me. If you don't believe music can have meaning, it's a fair question: telephone numbers, for example, are short on subtext and so rarely raise a laugh. Yet even numbers can be humorous to some people. Mathematicians say that numbers take on meanings, and some combinations can be genuinely funny. For most of us, though, such humour will seem arbitrary and personal - and isn't looking for humour in music an equally subjective pursuit? Of course not; it just takes a little understanding of the language of music, and Shostakovich was surely the great master at communicating through that language, with all the associations, nuances and references that music has.

Let's say that the three "primary colours" of humour are slapstick, exaggeration, and juxtaposition (of two incongruous situations). Just as red, green and blue combine to make any colour discernible to the eye, intensified by qualities such as brightness, context and texture, so all jokes, whatever their colour, are essentially a mixture of these, perhaps intensified by motivational and referential elements such as satire, puns, or in-jokes. Man slips on banana skin: slapstick. It's funnier if he's our boss: in-joke. Mimic does impersonation of someone dwelling on all their worst qualities: exaggeration. It's funnier because the impersonated is a politician: satire. When is a door not a door? When it's ajar: juxtaposition of the double entendre. It's meaningless unless you appreciate the double meaning involved: pun.

Context is vital too; we all know how humour and terror can each strengthen the force of the other. The gateman's speech on the problems of brewer's droop in Macbeth occurs just before the murder of Duncan, making the deed seem all the more terrifying. Conversely, humour in the form of black jokes is an effective catharsis in times of crisis: Russian jokes about bread queues and political incompetents are about the one item they do traditionally have in unlimited supply. (The stark six-point joke above seems to me characteristically Russian, with the sort of elements Shostakovich put in his music: satirical black humour, stark contrast to the extent of contradiction, and a tight, almost schematic, form to it.)

Do these primary colours of joke also occur in music? Of course. Take the above three examples. The banana-skin joke occurs all over the place in music: Haydn's bassoon that farts in an unexpected silence in the last movement of his Symphony No. 93; Mozart's horn players in the not particularly funny Musical Joke playing horrifically out-of-tune notes because the clot writing it didn't know how to write for their instruments; or Shostakovich's pianist in the first piano concerto who - while silently and obediently watching the "drunken trumpeter" lurch his way cheerily through the simplest of tunes - apparently falls asleep, crashing out onto the length of the keyboard and startling everyone. And is there an in-joke here, with the pianist as Shostakovich, the trumpet as some clownish party member spouting simplistic cant?

Exaggeration? You can't get much more inflated than asking for the same witless tune to be repeated twelve times in succession, but Shostakovich does that in the Seventh Symphony. The satirical element makes the joke, though: it's remarkably easy to picture the cheery tune as part of a whistle-while-you-work propaganda message which gets sung with progressively more gritted teeth over, and over, and over again, as the clouds of conflict and terror around it gather. It ends up looking utterly stupid and hollow, and whether you think it represents the Nazis moving in on Leningrad, Stalin's Terror, or just man's extraordinay talent for tolerating the rise of tyranny, the effect is the same. Like much, perhaps even most, of Shostakovich's musical humour, this is the sort where you either laugh or cry.

Grotesque juxtapositions occur so frequently in Shostakovich, from the "wrong-note" piano music of his earlier years to his references-within-quotes of his later works, that it's seen as a trademark of his. Take the cardboard cutout William Tell figure that unexpectedly appears in the middle of the first movement of the deeply three-dimensional Fifteenth Symphony. It never fails to get audiences smiling. (But I've never seen them laughing - was there a law passed about not laughing at concerts? Beethoven's First was played with cuts at its second performance because the conductor feared the audience would laugh, so they must have done it then. Still, that's a matter for another article.) But there's more to the quote than a Pythonesque surreality. Shostakovich, according to Ian MacDonald's The New Shostakovich, was known not as the "Soviet Beethoven"in the USSR, but the "Soviet Rossini", a purveyor of light but disposable music to order. The interpretation of it is endless, but one meaning is clear: whatever your achievements, you can't escape your past or your reputation.

So what of the Twenty-Four Preludes and Fugues? Like any great work of art, they are steeped (however consciously or unconsciously on the part of the composer) in the political, artistic, and personal climate of their time - and humour. There is also the whole gamut of human emotion - deep tragedy (Prelude No. 14), gritty war-film heroism (Prelude No. 6), wistful pathos (Prelude No. 5), relaxation (Prelude No. 23), springlike optimism (Prelude and Fugue No. 7), carefree cheeriness (Prelude and Fugue No. 17), inebriated merrymaking (Fugue No. 11) and crazy high spirits (Fugue No. 2) to take a few examples almost at random. But, as ever with Shostakovich, the key to understanding the meaning of the pieces - and therefore their artistic whole - is not merely in the "overall feeling" of any prelude and/or fugue. In any case, the "feelings" in one prelude or fugue can be contradictory. It is in the tension between conflicting ideas, which generates that extraordinarily dynamic feel of Shostakovich's music - the feeling that something's going on, that there are several forces battling to manipulate the music to their own ends as the piece progresses. That tension is so often revealed and sharpened up by the use of humour that recognising the "funny bits" in the Preludes and Fugues is often the first step to knowing what they mean.

Take the slapstick first of all. It's already shown up in the second fugue: after the (literally) pure whiteness of the first fugue in C major - which, astonishingly, doesn't contain a single accidental and therefore not a single black note - the second A minor fugue careers about all over the place, slipping on tonal banana skins everywhere and blundering into and out of unrelated keys with the crazy energy of a Keystone Cop chase (the sort Shostakovich must have accompanied dozens of times in the Bright Reel cinema as an impoverished student). A simple joke, but one heightened by the context (the purity of the opening fugue) and the in-joke (Shostakovich's life). Prelude No. 21 is similarly hilarious.

Exaggeration? What about the cheery fugal motif in the A flat Fugue, No. 17, which insists on introducing itself into every part of the keyboard it can - even down in the very bottom register, where conditions are so murky it sounds as if it has to pull a comically long face as it peers through the mud at us. Keep smiling at all costs, the piece seems to say: it brings to mind Shostakovich's purported comment in Testimony that he just kept saying "eighty-eight" repeatedly when photographed meeting people on official visits, because it made him look as if he was smiling and talking without having to go through the charade of small talk.

Exaggeration also shows up in the toyshop silliness of the wrong-note Prelude No. 8 in F sharp - the key of suffering and pain: this is music worked by strings. But the fugue following it is obsessive, anguished and nightmarish - definitely not kids' stuff at all. If the piece isn't saying anything, it's musical nonsense to have such disjoint moods next to each other. So what is the piece saying? Is it a statement on how some people are casually manipulated like puppets - following almost exactly the same pattern as the first two movements of the Fifteenth Symphony nearly twenty years later? If so, it's the funniness (in both senses of the word) of the Prelude that alert us to the message.

And dislocation? Take the Prelude No. 19 in E flat, Beethoven's heroic key. The opening is a solemn, thundering series of chords that sets us up for a grandly heroic theme over an E flat pedal - but instead of a fanfare celebrating the liberation of the people by socialism, all we get in response is a mocking little snigger that keeps coming back to nag at the fanfare-blowers whenever they try again, all the way through to the fadeaway end. The mechanics of the joke are simple juxtaposition, but it's a pretty thin joke unless you believe there are politically motivated characters behind the two musical adversaries. Once you've heard the Prelude that way, it's very difficult to believe that Op. 87 is Shostakovich's "least political work", an assertion I read to my dismay the other day. (Even more to my dismay, it had my name at the top of it.)

But if one Prelude and Fugue sums up what I'm trying to say about the set, it's No. 15, at 488 bars (206+282) by far the longest in the set. It is, arguably, more significant a statement than the 379-bar grand D minor Prelude and Fugue that finishes the work. When I first heard No. 15 (played by Barry Douglas on television in 1987) I burst out laughing. The "obviously funny" bits are a sarcastic prelude of overblown pomposity (exaggeration), some blatantly wrong notes at the end of the prelude (slapstick), a fugue of crazy intensity (exaggeration), and the bizarre ending of a very complicated piece plonking itself back into a very simple ending (dislocation). The more you look at the score, the funnier it gets, though somehow the effect of all the primary colours of humour together gets blacker and blacker. And as you identify the humour in the piece it seems to reveal a very clear message - a meaning - in the music.

When the prelude starts we're deep into the heart of the Twenty-four Preludes and Fugues, five flats and about an hour and a half away from our idealistic, almost innocent departure back in C major. A harshly metronomic minor third suggests the beating of a teacher's cane on a desk - is this some kind of lesson? If so it's clear we're required to sing along, and the bass duly obliges. (The first seven notes of the tune, bizarrely to Western ears, are those which open "We Wish You a Merry Christmas". Tatiana Nikolaeva, the dedicatee of Op. 87, doesn't know whether the resemblance was intentional - Shostakovich deliberately put several well-known Russian tunes elsewhere into the set, so it wouldn't be surprising, even though Christmas is not a Russian festival. However, the Prelude was written between Christmas and 30th December 1950 with the ground covered in snow, so the resemblance is appropriate if unconscious.)

The enforced, strident, but completely emotionless, nature of the first part of the Prelude No. 15 is disquieting. On goes the tune, stomping along in its brutal staccato triple time, with some witless nodding from a yes-man bass in shape of repeated G flat-F sequences. After forty bars or so of sound and fury that really signifies nothing at all we abruptly move into a lullaby, which even though phrased smoothly still manages to be quite empty of feeling. It's all a bit beyond the bass, which is still stuck in staccato yes-sir mode and can't really keep up. By the end of lullaby it's plodding up and down almost at random, and seems desperately grateful when the staccato opening stick-rhythm returns: now that's a tune I do know, it says, and gets carried away as we crash on to a grand conclusion - except that in the final three triumphant cadences, the half-wit bass is given his chance to stand up and do a brief solo in front of the class. He gets three chances but, of course, gets it completely wrong each time, blurting out an A natural, G natural, and then, worst howler of all, a D natural, all in a solidly tonal D flat - the flattest key imaginable. If you thought the prelude was serious all along, those three notes must convince you that in fact it was a totally sarcastic view of things.

If the prelude is in the classroom, the fugue is in the madhouse: the sheer demonic energy has brought most listeners to the same conclusion. After the prelude left us firmly in D flat major, in comes the voice of dissent: an overexcited, shouted, "mad" sequence of notes. It is in fact a curiously wedge-shaped tune that starts out as a twelve-tone row, but never quite makes it: ten or so notes into the sequence it begins to lose track of itself, and by the time its companion has taken up the same line excitedly, it is wandering aimlessly off, tripping and stumbling into nowhere. But the idea has taken hold, and voice after voice takes the idea up, so that we have a grimly comic bedlam - like scene of crazy soapboxers all haranguing each other in a furiously atonal fugue. (Fortissimo marcatissimo sempre al fine, the direction reads at the beginning.)

But suddenly, something extraordinary, and funny in both senses of the word, happens: the prelude interrupts (it happens nowhere else in the set) in the shape of that stick-beating staccato rhythm, as if the teacher had just burst unexpectedly into the room to quell the rabble. The mob's shocked silence lasts just two bars, however, before they all start again. But now they know they are being watched, and throw around "proper" cadential finishes to contrive to end the piece as if it were a straightforward tonal one, as if to please their superior. They manage it, eventually, but it's far from convincing - in fact, the bizarre juxtaposition of this unchained, spiky four-part fugue with the squat, glued-on ending is decidedly funny.

But the humour alerts us to the message. Some of the sanest people around can be found in lunatic asylums (that has been especially so in Soviet institutions, where political dissent was seen as a mental illness). On one level, the Prelude and Fugue No. 15 is about two irreconcilable systems - atonal and tonal music. That is undeniable; it is in the music. On another, it could well be about the treatment of dissidence. In the Prelude, the half-wit survives despite - in fact, is almost rewarded because of - his profoundly comical inability to do anything except clumsily repeat what he's heard. In the fugue, the dissenters are bullied into doing much the same. And that's not very funny at all.