Descartes laid the foundations of the entire edifice of modern Western philosophy on it, but David Cameron, we are now told, doesn't do doubt. A profile of the Tory leader in Time magazine, no less, this week quoted one of his closest friends as saying the 41-year-old Conservative Party leader has "mind-blowing confidence". He is ambitious, competitive, ruthless and possessed of an element of selfishness – "all the things which are important if you're going to be Prime Minister". And "he doesn't do doubt".
This isn't just the judgement of those closest to Cameron. Noting that much of Tory leader's strength derives from self-belief, the Time article goes on to quote the man himself, observing that what he possesses is not the fragile veneer of assurance acquired or affected by most politicians but a deep-down certainty that protects him from dark nights of the soul.
"There's no massive thing I've done," Cameron told the magazine's London bureau editor, Catherine Mayer, where "I lie awake thinking I wish I'd never done that".
Politicians are not supposed to do doubt. Dithering, the lowest grade of doubt, is the charge the Tories have successfully managed to pin on Gordon Brown in recent months, though the current Prime Minister seems not to be so much a ditherer as merely lacking the sureness of strategic touch that characterised his predecessor, Tony Blair, and which the Brownites at the time reviled as shallow. But we admire, even desire, confidence in our political leaders.
Yet there is something also rather scary about this preternatural confidence. Lack of doubt is what led Blair into Iraq. It is what, in our wider culture, leads us into unquestioning acceptance of ideological positions, such as that of the market, science, Communism or theocracy being the answer to every problem. But real life is too complicated to allow for single solutions; there is always some case to be made for the opposing point of view, as Western civilisation has known since the days when Socrates invented dialogue and dialectic. The market needs the common good, technology needs morality, the collective needs free individuals, churches need the common sense of secularity: the truth is never singular.
So why is doubt generally a dirty word within the political lexicon, with politicians unable to change their minds without being accused of doing a U-turn? Why do we prefer machismo to mature decision-making? "When the facts change, I change my opinion ... what do you do, sir?" asked the great economist John Maynard Keynes. Recent days have shown, with President George Bush's decision to nationalise the US mortgage giants Fannie Mae and Freddie Mac, that even bankers and Republican presidents believe in socialism when it is their jobs that are on the line.
The reality is that we need more doubt about, not less. We need politicians who will say, as Oliver Cromwell once did: "I beseech you, in the bowels of Christ, think it possible you may be mistaken." Mention of God leads us on to the other resonance in the idea of Cameron not doing doubt. The phrase echoes that of Alastair Campbell, who famously interrupted a journalist interviewing Blair with the words: "We don't do God." The irony was, of course, that Blair very much did do God, in private, which was where his advisers desperately sought to confine the deity.
The picture with Cameron is, like so much else about him, a good deal more fuzzy. He told an interviewer in a recent book that, on religion, he was a "pretty classic Church of England 'wracked with doubt and scepticism' believer". But he has offered so little else on this front that it is hard not to see this as part of his Demotic Dave stance to depict himself as a regular Everyman doing his best for his kids and getting them into a good church school.
Introspection isn't his thing, Time concludes, quoting him as saying: "I'm a very simple soul." He dismisses the notion that his ideas amount to a political theology that might one day be known as Cameronism: "I think you just get on with it. It's the best thing to do in politics rather than trying to endlessly work out the definition of who you are or what you're about."
His pragmatism touches something deep in the English soul, which has been there at least since the Elizabethan Settlement yoked Protestants and Catholics together in a workmanlike solution to the ideological ravings of the Reformation. Yet pragmatism, ironically, has its roots in unease with radical certainties. Doubt is at its heart, even as it underpins the very business of philosophy that, as Aristotle defined it, is "the art of doubting well".
Of course, doubt in philosophy is rather different from doubt in politics. Socrates, Plato tells us, sought to arrive at the truth through a series of questions, the answers to which gradually lay bare underlying beliefs that may then be exposed as mere prejudices. We wouldn't want too much of that kind of thing in modern dog-whistle politics. After all, Socrates's insistence that "the highest form of human excellence is to question oneself and others" was a sentence of death as surely as was Christ's radical injunction to love our enemies.
So it went on. "By doubting we come at truth," said Cicero. The medievals cherished the same approach. "The beginning of wisdom is found in doubting," said Abelard and the greatest scholastic, Aquinas, based the whole method of his Summa in such disputation.
Via Descartes, whose doubt became so universal that he questioned even his own perceptions before falling back on the certainty of Cogito ergo sum (I think therefore I am), this brought us to the modern scientific method, which doubts everything that it cannot prove. Doubt is even, as Cameron should know as a Conservative, at the core of the political philosophy which says that as little as possible should be done by the state.
Contrary to what many Dawkins-ites think, religion increasingly emphasises the strain of doubt that has been intricately woven into its fabric since the beginning. The institutional church has not been strong on doubt, nor are modern fundamentalists or anyone of those who have perpetrated all manner of outrage in the name of religious certainty down the ages. But doubt is at the heart of metaphysics. Faith is only possible in the face of doubt and uncertainty; remove the doubt, and faith becomes mere knowledge.
Faith embraces doubt, which is why in the early church Christ's other disciples didn't give Doubting Thomas the boot. As the Jewish poet Yehudi Amichai wrote: "From the place where we are right, flowers will never grow in the spring. The place where we are right is hard and trampled like a yard. But doubts and loves dig up the world like a mole, a plough."
Doubt is not the enemy; certainty is. And if we value doubt in our poets, academics and theologians perhaps we should look for it too in our police officers, generals and political leaders. And those who don't "do doubt" may be those who need to be questioned most. Though, of course, I could be wrong about all this.