When Eliot Spitzer, the Governor of New York, appeared before the media after being heard, on an FBI wiretap, arranging a tryst with a prostitute, he apologised for having “acted in a way that violates my obligation to my family and violates my, or any, sense of right or wrong”. This form of words implies that his fault was to seek paid-for sex, and no doubt plenty of people agree, chiefly those who are for marital fidelity or against prostitution or both.

But what made it impossible for Mr Spitzer to remain in office, despite trying to describe what he did as a private matter, was that during his public life he presented himself as a moral crusader. He gained a reputation as an anti-corruption campaigner who, in two terms as New York State's attorney-general, not only exposed financial shenanigans on Wall Street but dismantled two big prostitution rings, in the process proclaiming his revulsion and anger at their existence.

In short, Mr Spitzer's chief crime was hypocrisy. If anyone ever needs a clear-cut example of this failing, Mr Spitzer provides it - as does the “Praise the Lord” preacher Jim Bakker, brought down by scandals about alleged rape and fraud, and, even more so, Jimmy Swaggart, who exposed Bakker and described him as a “cancer in the body of Christ”, only to be himself found consorting with prostitutes. (Memorably he told his congregation, after the revelations, that “the Lord told me it's flat none of your business”.)

In all these cases public professions and private behaviour not only contradict one another, but do so in a particular way. The public professions are claims to virtue and high standards, yet the private behaviour consists of what the public professions proscribe. If someone publicly supported prostitution but privately did not engage the services of prostitutes, no one would call him a hypocrite. It is the twofold fact that virtue is claimed, but dishonestly and consciously so, that is the key. In its original Greek meaning, “hypocrite” meant an actor, and was a morally neutral term; it has gained its pejorative meaning because the acting in question is such a repulsive lie.

All this said, Spitzer-type cases have the unfortunate consequence that many cases of failure to live up to ideals are misidentified as cases of hypocrisy, and - even less fairly - the word gets misapplied to examples of human frailty (or just to human nature expressing itself in all the naturalness of its needs and desires) when in fact there was no claim to special virtue in the first place.

Politicians and preachers are the prime targets for accusations of hypocrisy, almost exclusively in matters of sex and money. True, they have only themselves to blame if they pretend to live by high moral standards and then find front pages of newspapers covered with photographs of themselves sucking toes not attached to their wives.

But there is a difference between people who lay claim to such virtue but who practise what they themselves define as its opposite, and those who make no such claims. Many people assume that certain public roles automatically carry with them expectations of traditional sexual virtues, and in some cases they are right - for example clerics, school teachers, doctors - and in some cases not right - for example politicians (unless they proclaim themselves squeaky-clean), city traders, bus drivers.

If the charge of hypocrisy is bandied about too much, it masks the important fact that there is no dishonesty, and no shame, in sincerely wishing to attain certain ideals, but not getting there. That, after all, is a common human experience. The philosophers of classical antiquity endlessly discussed the problem of “knowing the better but doing the worse”, which some thought of as a product of weakness of will, others as self-deception, others as a fact about the difficulties, constraints, temptations and complexities in the human condition.

The key word is “sincerely”; the central feature of hypocrisy is precisely the lack of sincerity. And of course it is easy for people insincerely to claim sincerity, as yet another layer cloaking their hypocrisy. But although people can hide from the nastier truths about themselves for long periods, there is some satisfaction in knowing that not everyone can do this completely, and that especially includes hypocrites. Knowing that one has been hypocritical about something is no small punishment in its own right.

In their relentless pursuit of sensation and scandal the media are always too quick to describe ordinary failings as hypocrisy. There are familiar cultural differences in this; French newspapers would only label a married politician as a hypocrite because he or she has a lover if that politician had publicly advocated marital fidelity. In our Anglo-Saxon world with its adolescent, sniggering and apprehensive attitude to anything sexual, it does not matter whether a politician has said anything at all about sexual morals; a mistress, a prostitute, a visit to a gay bar means open season.

It would be refreshing if the Spitzer case focused attention on the real meaning of hypocrisy, thus putting a limit on the hypocritical use of “hypocrisy” as a blanket witch-hunting term in the moral sphere. We might all be able to think more clearly and judge more fairly as a result.

A.C.Grayling is Professor of Philosophy at Birkbeck, University of London

Times Recommends

• Nerdy cafés no longer maid in heaven
• Cameron will not break marriage vow
• Avatar will make the case on climate