Leading article: Joe Public, the lie-detector in the street

How is it that both John Major and Tony Blair sound more convincing when accusing the other of lying than they do when saying where they themselves stand? It has not been an edifying week of the election campaign, with words like "despicable" and "bare-faced" traded, both sides shouting "Pants on fire!" in their best grown-up voices, and Paddy Ashdown, as ever, shaking his head like a pained and disapproving teacher surveying the unruly playground.

But would the Conservatives scrap the state pension? It sounds possible, when set against Peter Lilley's ambitious and complex plans for recasting the basis of pension provision by the middle of the next century. Would Labour put up taxes in an July Budget? It sounds plausible, notwithstanding Gordon Brown's patient explanation that there are no hidden spending plans to require such a thing. There is a directness and a simplicity about the charges which make them sound as if they - might - express some kind of truth, even if they are not borne out by the formal policy positions of the two parties.

And it is, as Mr Major discovered yesterday, frustratingly difficult to rule out absolutely a hypothetical future decision. What if, he was asked, the Cabinet overruled him to abolish the state pension? "If anybody in my Cabinet actually prevailed in an argument, I would not only leave Downing Street, I would leave politics and I would call a general election," he replied, finding himself perched rather awkwardly up a hypothetical gum tree.

Of course, it is grossly unfair to say that the Tories will abolish the state pension, when they want to replace it with a state guarantee of a pension of the same value. Mr Blair is playing with words. But, as our front page report confirms, he is not (quite) lying.

The Tories are scaremongering too. Mr Brown has to have a Budget in July in order to bring in his windfall tax (of as yet unknown size) on the privatised utilities, and to cut VAT on domestic gas and electricity from 8.5 to 5 per cent. To describe this an "emergency" Budget, as Tory politicians do, is dishonest, and all Labour's pledges are indeed paid for either by the windfall tax or by clearly-labelled savings elsewhere. But to speculate that Mr Brown might make other tax changes at the same time is fair speculation and has not been denied.

The dangers of this kind of exaggeration and name-calling are obvious. The voters are already cynical and alienated. As Mr Blair often points out, negative attacks tend to induce apathy and a "plague on all their houses" mentality. But let us not become sentimental about this. After all, despite letting it be known that he had "ordered an end to negative campaigning" early on in the hustings, there is no sign of High Moral Tony now.

Anyway, election campaigns should be aggressive rather than sanctimonious affairs. Accusing the other candidate of lying is as old as democracy. As Henry Mencken said: "Under democracy, one party always devotes its chief energies to trying to prove that the other party is unfit to rule. Both commonly succeed, and are right." He could have added, but didn't, that one is usually at least a little less unfit than the other.

No doubt Pericles had a few shocking words about his opponents' policy on the price of slaves when Athenians cast their pebbles in the earliest democracy. The founding fathers of American democracy called each other much worse than liars. John Quincy Adams called Thomas Jefferson a "slur upon the moral government of the world". Disraeli and Gladstone insulted each other with more wit and imagination, but certainly with as much contempt as Major and Blair.

Everyone knows, even if they sometimes pretend to a more elevated discourse, that politicians "go negative" because it works. American political scientists have even conducted experiments to prove that voters are more likely to remember negative information than positive virtues. That is because we voters are sceptical about politicians, and always have been. And so we should continue to be. Scepticism is part of the essential armoury we need to try to defend our interests. And we need, in the age of mass communication, to find new ways of assessing the reliability of our would-be leaders.

That is why this campaign has been so dominated by the respective struggles of Mr Major and Mr Blair to appeal directly for the trust of the voters. All of politics nowadays is a search for sincerity, an attempt to construct authenticity in an age of mass communication. In the past 10 years, all politicians have taken to the "sincerity machine", or glass tele-prompter. In this campaign they have realised that they look even more sincere if they can manage a planned ad lib, breaking off from the rostrum. Tony Blair's biopic was deliberately rough-edged, to try to convince us that it was more ``real'' than a glossier production. But as the politicians and their advisers construct, so their audiences deconstruct. We are communication experts, attuned to the tricks and artifices of film, just as earlier generations were familiar with the tropes of traditional oratory.

In the end, dodging through angry exchanges, and the mimicry of anger; spontaneous off-the-cuff explanations, and the mimicry of spontaneity; touching artlessness, and carefully prepared, learnt artlessness, we can only go on our guts, our instincts. We yearn to believe in character, and, despite ourselves and our long experience, we thirst for authenticity.

In the end, that is the saving grace of abusive press conferences and tetchy interviews. For as these men get angrier, they expose more of themselves. Pressed by impertinent interviewers, they sometimes forget their training and preparation. The guard slips, a flash of more than make-up can be seen glowing on the cheek. We may tut-tut, but we watch these moments avidly. For time is running out and watching is our duty.