Why are we asking the question now?
Because the fifth series of Celebrity Big Brother, one of the biggest hits in reality television, got under way on Channel 4 last night. The veteran film director Ken Russell, 79, the actress Cleo Rocos and a clutch of pop stars old (former Jackson Five singer Jermaine Jackson and Leo Sayer) and newer (Ian "H" Watkins, formerly of Steps, Jo O'Meara, ex-S Club 7, and Donny Tourette of the Towers of London) entered the Big Brother house to fight it out in the public's affection over the next three weeks.
The line-up was completed by Carole Malone, a journalist, Danielle Lloyd, the former Miss England and the girlfriend of England footballer Teddy Sheringham, Dirk Benedict of The A-Team, and Shilpa Shetty, a star of Bollywood.
What is reality television?
Reality television is a genre of unscripted programmes that present real events rather than fiction, featuring "ordinary" people rather than actors. The current explosion began in 2000 when the first series of Big Brother was broadcast on Channel 4. However, the online encyclopaedia Wikipedia points out: "Critics of the genre have claimed that the term is a misnomer, as many reality TV shows put the participants in exotic locations and/or abnormal situations". And the celebrity versions obviously include "stars" - sort of.
Who loves reality TV shows?
Millions of viewers - about 10,000 people sent in video applications to join the Big Brother house last year - plus tabloid newspaper editors and showbusiness gossip magazines who fill acres of space with the antics of participants.
"If you're interested in human interaction then reality television is the genre that deals with that," says Boyd Hilton of Heat magazine. "They're unscripted and unpredictable and that's what makes them exciting." It is snobbish to dismiss such shows because they are popular, he says.
Who hates them?
The likes of John Humphrys, the presenter of Radio 4's Today programme, and Paul Watson, ironically, the producer many credit as the godfather of the genre with series such as The Family in 1974 and Sylvania Waters a year earlier. Humphrys, in his MacTaggart lecture at the Edinburgh Television Festival in 2004, condemned the "coarsening effect" of reality television.
"That's partly because of the sheer vulgarity. But it's even more that it turns human beings into freaks for us to gawp at," he said. "This is not just bad television in the sense that it's mediocre, pointless, puerile even. It's bad because it is damaging."
Paul Watson has condemned channel after channel for showing reality TV. "It's predictable. It doesn't inquire, it doesn't upset, it just creates more of the same and makes our film makers lazy."
Charles Allen, the departed head of ITV, also argued Channel 4 should be doing more than "wall-to-wall Big Brother in prime time".
Is there not a law of diminishing returns?
It would appear not. While some shows have failed to flourish, notably Celebrity Love Island, many are now bulwarks of the schedules. Last year, the opening night of Celebrity Big Brother, starring George Galloway, Rula Lenska and a then-unknown Paris Hilton look-alike called Chantelle Houghton, who eventually won, attracted 6.5 million viewers and more than a quarter of all viewers at the time. At its peak, the show was watched by 7.6 million viewers, a 31.2 per cent share of the audience.
Big Brother did even better. The 2006 final attracted 8.2 million viewers at its peak, a 45.6 per cent share of everyone watching television at the time. This was higher than the year before which averaged 6.7 million viewers and a 34.4 per cent share, peaking at 7.8 million.
They have inspired and influenced dozens of others. A couple of years ago, Channel 4's I'll Do Anything to Get on TV claimed there would be 176 reality TV shows on screen that year.
Are reality TV shows trash or treasure?
Alongside the low-brow, expletive-filled antics of the Big Brother house, there have been some attempts to use the genre for good. In Jamie's Kitchen and Jamie's School Dinners the chef Jamie Oliver offered jobless youngsters the chance to train and lead a nationwide campaign to improve the quality of school meals.
And they have arguably reinvigorated other programmes. Everything from BBC2's business shows, Dragon's Den and The Apprentice, to Channel 4's Secret Millionaire, where real-life millionaires go undercover to find a worthy beneficiary for some of their riches, have been influenced by the notion of real people on screen. "Producers know they have to make much more sophisticated, faster-moving programmes now," Boyd Hilton says.
What about the rest of the world?
There are now Big Brother houses in more than 20 countries. Ruth Wrigley, of Endemol, once claimed each version conformed to national stereotypes. "The Germans were very efficient at doing their tasks, the Scandinavians shagged like rabbits and the producers had to tell them to stop, the French were very romantic and the Spanish were fiery. The British were very British and drank cups of tea and sat round the table talking."
Can reality TV last?
Yes. Commentators such as Boyd Hilton think they are definitely here to stay. "Readers are excited by stuff that is happening right in front of their eyes," he says. The broadcaster Krishnan Guru-Murthy has described the genre as "a firm and embedded part of television's vocabulary, used in every genre from game-shows and drama to news and current affairs".
Mathew Horsman, the joint managing director of the research and advisory company Mediatique, says reality television is part of the trend throughout the developed media world towards participation, whether online with MySpace and YouTube or through interactive television shows with public votes. "Perversely, because the big reality TV formats are 'live', they become event TV and people tune in to watch. They don't time-shift Big Brother or Strictly Come Dancing. This is water-cooler stuff," he says. "I am absolutely convinced that reality TV will continue to have a life."
The only question is whether reality television programmes might eventually migrate from network television to the internet. "That must be the broadcasters' biggest fear and why Rupert Murdoch bought MySpace and ITV bought Friends Reunited," says Mr Horsman. In the meantime, though, reality TV has one other major virtue - at least for broadcasters - it's cheap to make.
Should reality TV be applauded?
* It entertains millions and has reinvigorated television at a time when viewers have growing choices
* The revenues generated help support other, more heavyweight programming in the schedules
* The campaign unleashed by 'Jamie's School Dinners' illustrates how audiences can be harnessed as a force for social good
* It turns participants into public freaks and has contributed to a coarsening of standards on television and in day-to-day life
* The reality aesthetic has invaded all areas of programming, so that no subject can be tackled without public participation
* It contributes to our dubious fascination with fame, in which people are celebrated not for accomplishments but for being on TV