The columnists and pundits who remarked at the weekend of Eric Cantona that to kung-fu kick one person might be regarded as a misfortune, but to kung-fu kick two looked like carelessness, were merely the latest example of cultural homage to Lady Bracknell's Act One comment about John Worthing's loss of both his parents. (On the same day, Washington commentators were to be found adapting the Bracknellism to President Clinton's nomination of two successive contentious candidates for Surgeon General.)
A play can live on through allusion and quotation in the general culture - as many of Shakespeare's do - without a wide enthusiasm to see it in performance. The Importance of Being Earnest, though, is British theatre's greatest commercial certainty. Why has this drama sustained such love through the century of Valentine's Days since it was first cheered?
Some of the passion for the play is, it must be admitted, practical or negative. The Importance of Being Earnest is regarded as an artistically safe play: no sex, no swearing, no violence, no politics. Written in the late 1890s at a time when the vocabulary of English had solidified into something close to what is spoken now, it is friendly to a modern ear in a way that 18th-century comedy often is not. Requiring nine performers and two living-room sets, it is a cheap and easy bet for regional and amateur theatres, although in fact the successful delivery of the text's relentless epigrams is one of the stiffest tests of acting.
The literary importance of The Importance, however, rests on anything but safeness. Wilde's text was virtually experimental in being perhaps the only comedy in history in which nearly every line, even of exposition or explanation, is a joke or a cue for a joke.
Prominent is the kind of epigram with which Wilde's writing is most associated, particularly in what might be called four-part disharmony, such as: "All women become like their mothers. That is their tragedy. No man does. That is his." This trick also frequently takes the form of inverted common wisdom, as when Gwendolen laments: "Few parents nowadays pay any regard to what their children say to them. The old-fashioned respect for the young is fast dying out. Whatever influence I ever had over mamma, I lost at the age of three."
The other Wildean trademark is metaphorical over-reaction, as when the news that John Worthing was found abandoned in a handbag at Victoria Station leads Lady Bracknell to object: "You can hardly imagine that I and Lord Bracknell would dream of allowing our only daughter - a girl brought up with the utmost care - to marry into a cloakroom and form an alliance with a parcel."
These joke structures are the foundation of 20th-century theatrical comedy in English. The line of descent from Wilde through Coward and Orton to Stoppard and Bennett is a clear one: each reworks the templates of Wilde's epigrams and exaggeration arias.
Stoppard openly acknowledges the genealogy in Travesties, which is a parody of The Importance of Being Earnest, but a quieter debt is just as apparent in Arcadia when the overbearing Lady Croom comments of her precocious daughter: "Thirteen years and ten months. She is not due to be pert for six months at the earliest, or to have notions of taste for much longer."
But Wilde's shadow is not limited to theatre: ambition towards his tradition is just as evident in the television scripts of Galton and Simpson, John Cleese and Ben Elton. Indeed, The Importance of Being Earnest reads like a compendium of possible modern comic forms. There is the simple pun - a reference to the virtuous "washing their clean linen in public" - and the dirtier word-play, as when Canon Chasuble remarks: "Were I fortunate enough to be Miss Prism's pupil, I would hang upon her lips
Though the social world of his comedy is lost, Wilde seems to us a very modern writer. The subject, and plot motor, of The Importance of Being Earnest is pretence and deceit. The theme is treated frivolously - although Wilde wrote a darker fourth act, in which Algernon faces arrest for running up debts, which the director cut from the first production - but it anticipates an obsessive concern of art and life in the 20th century.
Indeed, the double life was very much Wilde's subject. The central image in his novelistic reworking of the Faust legend, The Picture of Dorian Gray - of a portrait decaying in the attic while its subject fools the public with his surface beauty - has become a key myth in modern culture. The terrifying reminder in the attic underlies, tacitly or implicitly, much modern biography, political cartooning and social gossip.
This fascination with duplicity, expressed in comedy or horror, underlies the continuing appeal of Wilde's writing. It also helps his reputation that his work and life are perfectly suited to an age in which biography is the dominant literary form: in which readers are encouraged to see all literature as either transcription of autobiographical reality or willed denial of it.
Although the actual biography of Wilde published by Richard Ellman in 1987 was considerably more subtle in its connections, the author of The Importance of Being Earnest matches in the public imagination the popular image of an artist. Beneath the public wit and dazzle was - as convention now dictates is always the case with the witty - a private darkness. It is hard now to see The Importance of Being Earnest, knowing what we know about the author's sexuality, without reading into its embarrassments of men pretending to be other men a kind of frantic code.
As it happens, the play was premiered on the eve of Wilde's destruction. His wife was reported to have mirthless tears in her eyes on the opening night of a play which made most weep with laughter. A police presence was posted against the attendance of the Marquess of Queensberry, against whom Wilde had launched the libel suit that would begin his ruin. There has rarely been a starker example than that opening night 100 years ago of the dissonance between a work and the circumstances of its production. The play, however, set the bench-mark against which English dialogue comedy would be judged for the next century and beyond.
Some gag writers can successfully imitate Oscar Wilde. That is their tragedy. Others can't. That is theirs.