There's less to laugh about now, and it shows

Changes in society over the past century mean that whole areas of life, such as class, are generally off the agenda for comics. Satire has replaced joke-telling

The Crazy Gang, hamming it up in 1941, 10 years after several acts joined forces (Rex)

My grandfather John William Taylor died 10 years before I was born but, in the 1920s, under the stage name of T T Taylor the Popular Comedian, he was a fixture on the local concert-party circuit. One, at least, of his jokes has survived: "My wife, she's so thin that when she drinks tomato juice she looks like a thermometer." Some years ago I tried this out on a friend who writes radio comedy shows. His judgement was emphatic. "It's too funny," he pronounced, meaning that a wisecrack of this magnitude would work against the person telling it by disrupting the performance's even flow.

I thought of T T Taylor the Popular Comedian, and the photographs of him in "character sketches" that still sit on my mother's mantelpiece, when reading the reports from this year's Edinburgh Fringe, and, in particular, the "top 10 funniest jokes" as judged for the television channel Dave. The list was headed by "I heard a rumour that Cadbury is bringing out an oriental chocolate bar. Could be a Chinese Wispa" (Rob Auton), "I used to work in a shoe-recycling shop. It was sole-destroying" (Alex Horne), and "I'm in a same-sex marriage... the sex is always the same" (Alfie Moore).

No disrespect to these titans of the modern stand-up stage, but none of their gags seems as funny as T T's master stroke. Taken together, they confirm a suspicion that has stayed with me ever since I first sat down to watch some "alternative comedy" – that is, people swearing in loud voices – back in the 1980s. This is that the present age is not a good time to be a comedian, if only because the social and moral changes of the past half-century have left the professional humorist with very little room for manoeuvre. Gags will still be minted and snooks cocked at establishments and vested interests, but the comedian who doesn't happen to be a maverick genius will always be constrained by the lurking awareness that, mysteriously, there is hardly anything left to be properly funny about.

To apply a conceit first dreamt up by the liberal historians of the 20th century, there are two main theories of comedy: Whig and Tory. The latter insists on the survival of comic elementals which endure whatever the social conditions that prevail around them, gets its greatest kick out of slapstick and believes that someone falling over on a banana skin is ipso facto funny whether caveman or cyborg. The Whig theory, on the other hand, maintains that humour changes over time and that, with humanity (allegedly) waxing more enlightened from one year to the next, what amused our great-grandparents' generation might not necessarily amuse us. Whether or not one accepts this distinction, the fact remains that much of the humour that would have been acceptable on a variety hall stage 70 years ago has either been superannuated or has reinvented most of its original features.

Part of this is to do with changing moral codes and assumptions. There is no point in the 21st century making jokes about adultery (about which we are all supposed to be terribly relaxed) or courting couples or the embarrassments suffered by honeymooners in seaside hotels. Even those staples of the bygone comic postcard, the mother-in-law and the lodger, have sunk into disuse in a world where most middle-aged women look more like fashion plates than ogresses and the paying guest has gone the way of the passenger pigeon. Another part is to do with the orthodoxy which insists that certain minority groups are not to be discriminated against, meaning that, outside a golf club, you cannot tell jokes about black people, the Irish, Jews, homosexuals and a few other constituencies besides.

But a third part is to do with the separations of taste and demographics that began to kick in during the early 1960s, when what had been a more or less homogeneous comic mainstream began to fragment into half-a-dozen radically distinct genres. My father, for example, who had grown up on the antics of the Crazy Gang, liked the Goons and relished the satire of That Was The Week That Was, drew the line at Monty Python's Flying Circus. "College kids, isn't it?" he would mutter. The same cordon sanitaire was erected around Blackadder, in which he diagnosed a self-conscious undergraduate tendency to show off. Naturally, quite a lot of this winnowing process was to be roundly applauded, especially the blanket ban on jokes about ethnic minorities, but its cumulative effect was drastically to reduce the volume of raw material left for comedians to exploit. Class, for example, a mainstay of English humour, in whose absence the English novel would perish overnight, is generally approached in a spirit of extreme timidity, and even the first law of British comedy – that foreigners are funny – has trouble surviving in an age when neighbours may not speak English as a first language.

Lashed, proscribed and institutionalised, subject to all kinds of official and unofficial censorship, the modern comedian is frequently boxed into a corner. Most of the time he or she is not funny, and he knows it. All that is left is the wisecrack – something that ruined American humour decades ago – and the cultivation of idiosyncrasy. In these circumstances, the most successful modern comedians tend to be not joke tellers but satirists engaged on the much more difficult task of projecting a personal myth, such as a delight in their own rectitude and importance that the viewer cannot share. Steve Coogan's Alan Partridge is a perfect example of this: the man desperate to impress his personality on the world around him, but always hamstrung by sheer ineptitude, lack of personal resonance, a sneaking awareness that he is not up to that world's fighting weight. It scarcely needs pointing out, of course, that Tony Hancock – and countless others – got there first.