Paul Vallely: The overwhelming power of music

Nick Clegg is not the only one moved to tears by melody and harmony. We are hardwired to respond to their perfection

To my ears, it sounded like a time capsule from another era. But tears formed in the eyes of my aunt as she listened on the battered old walnut-veneered phonogram which took pride of place in her front room. The singer was Enrico Caruso, and the aria, I think, was from Pagliacci. Operatic airs were the pop songs of her youth; Caruso was then only the second recording artist ever to sell a million copies. To me, it was alien if virtuosic. But to my aunt it laid bare the tragedy of a clown whose love was so jealous that he murdered his wife. I was nine; she was in her forties. We were listening to the same thing, but we heard something very different.

The tragic commedia dell'arte figure came back to my mind the other day, via the lyrics of an old Smokey Robinson song. "Just like Pagliacci did, I try to keep my sadness hid/ Smiling in the public eye? But in my lonely room I cry/ The tears of a clown...". Only this time it was "The Tears of a Clegg", after the Deputy Prime Minister gave an interview designed to reveal his softer side by letting slip the admission that he "cries regularly to music". Actors have feelings too, as Pagliacci would have it. If there's a smile on my face, it's only there trying to fool the public, in the words of Smokey Robinson.

Political pundits swiftly added what they called "the blubbing" to Nick Clegg's previously stage-whispered regular-kinda-guy confidences. Remember when he told Piers Morgan he'd had "no more than" 30 lovers? Or disclosed on Desert Island Discs that he is a secret smoker – and told the nation that he hoped his three children would not find out? But when it comes down to fooling you, now honey that's quite a different subject, but don't let my glad expression, give you the wrong impression... really, I'm sad.

Tears provoked by music can be profound or sentimental. Turgenev has a rhapsodic summary of the impact of music on the human soul when he writes of his hero in Home of the Gentry: "The sweet, passionate melody captivated his heart from the first note; it was full of radiance, full of the tender throbbing of inspiration and happiness and beauty, continually growing and melting away; it rumoured of everything on earth that is dear and secret and sacred to mankind; it breathed of immortal sadness and it departed from the earth to die in the heavens."

But tears can also flow from a more sentimental level. Strange how potent cheap music is, as Noël Coward observed. Mawkish melancholy moistens the eyes very effectively, sometimes against our better judgement. A phoney state of mind creeps in, as Roger Scruton has noted, and invites us to sympathise with a state of mind that, in our better moments, would seek to shun. He was writing about Andrew Lloyd Webber, though the barb might be aimed at other composers who have nothing to say and know well how to say it.

It is not clear what makes Nick Clegg cry. His office declined to elaborate on his aside in his New Statesman interview with Jemima Khan. The eight pieces he chose for Desert Island Discs recently offered a typical politician's balanced ticket to imply the widest electoral appeal. Presumably the Chopin Waltz in A Minor, which his wife played when she was pregnant with their first son, is a more obvious candidate than his selections from Prince, Radiohead and David Bowie. But there is always the chance that Johnny Cash's grim hominy homily "Sunday Morning Coming Down" could tweak the tear ducts in a self-pitying way.

Does it matter? Plato would say so. Music for the father of philosophy is not a neutral amusement but a vehicle for nobility, dignity, temperance, chastity. It has a moral character, and its style can influence those who embrace it. Scruton is interesting on this too. In a culture where pop stars are first among celebrities, idolised by the young and courted by politicians, something of their message will rub off on the laws passed by the politicians who admire them. "If the message is sensual, self-centred, and materialistic... then we should not expect to find that our laws address us from any higher realm," he says.

Music may predate language. Archaeologists have found instruments played by Neanderthals at least 50,000 years ago. Today, people with dementia or head injuries retain musical ability. Major keys and rapid tempos induce happiness, whereas minor keys and slow tempos bring sadness, while rapid tempos together with dissonance cause fear. Tests show that infants as young as four months show negative reactions to dissonance.

Do we learn this, or is it intrinsic? For centuries people have thought that the power resided in the notes themselves. In the 11th-century church, musicians found that moving down a semitone to the diminished fifth created a creepy dissonance. That tritone leap became known as the Devil's Interval and was banned. It still sounds spooky today, whether in Wagner's Götterdämmerung, Saint-Saëns' Danse Macabre, Jimi Hendrix's Purple Haze or Black Sabbath's eponymous first single.

Certainly it is possible to measure the impact of all this using brain scans. Dissonance increases activity in the paralimbic regions associated with emotion. Classic tingle factor pieces, such as Barber's Adagio for Strings, stimulate the regions of the brain which register intense pleasure and arousal, normally triggered by food and sex.

But all these could be learned associations. Mahler as a child ran into the streets to escape one of his parents' violent arguments and encountered a brass band. In his music, the brass is always linked to intense and anguished emotion.

When we undergo a trauma the brain makes a "recording" of all the other things that were going on at that heightened moment, Professor John Sloboda of Keele University has written. When we hear music, we replay the emotions we experienced when we first heard it.

But we learn from non-traumatic experience too. Half a century ago, the music theorist Leonard Meyer drew attention to the importance of expectation in the way we listen. We do not come to a new work as a blank slate. We have learnt forms from previous music. The emotional force of music comes from the way composers choreograph our expectations – sometimes delaying, teasing or thwarting the outcome we expect. Our brains are what Daniel Dennett called "anticipation machines". Music plays games with them.

"The distance seems to open up between who you really are and the portrayals that people impose on you," Nick Clegg, in his recent interview, said of the reality of politics. The reality of music opens up a gap that is far more profound. The depth of possibility is what music plumbs in the human soul. But it can also shine a sudden light into the chasm between what we might have been and how far we have fallen short of our potential. That is why music makes us cry. Some of us, of course, have more to cry about than others.