Perhaps the defining feature of a difficult subject for comedy is that many people consider it to be "no laughing matter".

Certain subjects are more or less taboo according to their perceived potential for causing upset or offence. For example, anti-semitic or otherwise racist jokes that might have been assumed inoffensive in the prevailing monoculture of early 20th century Britain, became broadly unacceptable as the cultural landscape changed. Meanwhile some subjects, such as death, remain universally "difficult".

SHOULD TABOOS BE TACKLED?

Arguably comic writers are right to test the boundaries of the acceptable. For example:

• Satirical comedy has done much to level the general public with the powerful institutions of church and state that seek, or at least have sought in the past, to exercise absolute control over thoughts and actions;
• Comedy about sex has played a major role in banishing the hypocrisy and prurience that were once such a prominent feature of British society.

INSIDERS VS OUTSIDERS

"Write from your own experience" may be good advice in general terms, but it is arguably crucial when it comes to joking about difficult subjects.

For example, anyone who jokes about a religious or ethnic group of which s/he is not a member is immediately on dangerous ground. Any joke that projects a negative image of the group is unlikely to be acceptable at all if told by an outsider, whereas an insider may get away with a joke that presents an authentic case for self-mockery within the group.

Conversely any joke that portrays the group as superior is likely to be acceptable regardless of who tells it. Indeed, jokes at the expense of rival groups are very much the accepted norm at partisan gatherings, such as club dinners and professional meetings.

In a free society, however, everyone is free to make jokes about groups that are widely perceived as deserving of ridicule, whether such groups are self-appointed, deliberately exclusive, inclined to take themselves too seriously or downright unlawful. Celebrities and politicians are probably routinely offended at the jokes made about them but, notwithstanding the laws of libel, they are seen as fair game because they freely court publicity. Secretive or otherwise obscure groups such as freemasons and animal rights activists are equally valid subjects for outsiders' humour because their motivations and methods are so little understood by the general public.

TRULY DIFFICULT SUBJECTS

The range of subjects which are truly "difficult" is extremely narrow, and very much focused on deeply felt personal issues such as identity, belief and mortality.

People are generally offended by jokes that seem to ridicule their ethnic origin, sexual orientation or religious belief, for example. Such jokes can be downright dangerous if they offend powerful or wealthy individuals who might resort to legal or physical reaction.

Jokes about fear-inducing subjects such as sickness, injury, war, terrorism and death may not be so much dangerous as tasteless. The degree of offence taken is strongly subjective, but is broadly correlated to how "near the knuckle" the joke is. For example, many westerners still consider the subject of 9th September 2001 to be off limits. And yet jokes become possible as events eventually assume mythic status: nearly a century on, for example, it is permissible to joke about the Titanic disaster.

And even jokes about death are widely acceptable when they are made at the expense of villains: think of Robert Maxwell falling off his yacht. The key factor here is that such jokes are based on the premise that evil comes to those whose behaviour is unacceptable.

The insatiable demand for topical humour has led humorists to develop sophisticated ways of dealing with difficult subjects. For example, the recent Iraq war, for all its seriousness, was the subject of many truly funny cartoons and comedy sketches. Arguably, the success of such humour lies in its careful circumnavigation of the truly difficult subject at the heart of the matter - death - focusing instead on the satirical and genuinely funny aspects of the war, such as the stand off between France and Britain, the elusiveness of the Weapons of Mass Destruction and the blatant misinformation peddled by the Iraqi minister of information.