One of life's great pleasures is to curl up with a good bad book. You're going to be utterly absorbed, moved and delighted, but you won't have to think very much. You may be alarmed or even horrified, but in the end justice will be done and the nice guys will win. You may not learn much about life, but you will find life just that little bit more bearable.
That's the feeling you get from a good bad book, but it's harder to define exactly what it is, or to give examples. The phrase was first coined by G. K. Chesterton and taken up most memorably by George Orwell in his essay, Good Bad Books.
Orwell defined his subject as ''the kind of book that has no literary pretensions, but which remains readable when more serious productions have perished''. He divided these books into two further categories: escape literature, and that which is ''quite impossible to call 'good' by any strictly literary standard''.
One of the effects of changing taste is that in the 1940s, Orwell was saying something quite subversive and daring. Today, he merely seems to be saying the obvious. We accept that works such as the Sherlock Holmes stories, the novels of Jules Verne and Alexandre Dumas, Rider Haggard yarns and Bram Stoker's Dracula are classics, even though they are also escapist entertainment. Time dignifies many penny dreadfuls and pulp fictions and renders them respectable.
But in Orwell's time, there was an almost insurmountable barrier between literary and genre fiction. Arthur Krystal surveyed this history in an essay in The New Yorker in 2012, when he resurrected Edmund Wilson's scathing piece on detective fiction, Who Cares Who Killed Roger Ackroyd? Reading mysteries, Wilson complained, ''is a kind of vice that, for silliness and minor harmfulness, ranks somewhere between crossword puzzles and smoking''.
Today, that sort of literary blindness is very nearly cured, though you still get the odd myopic comment from time to time. We revere mystery and thriller writers such as Raymond Chandler, Elmore Leonard and John le Carre as literary figures. Many more writers in the genre, such as Dennis Lehane and P. D. James, get solemn analytical reviews in the books pages and blogs; in Australia, Peter Temple wins the Miles Franklin award; and in the US, Stephen King wins a medal from the National Book Foundation for his distinguished contribution to American letters. This is pulp with prestige.
Other genres gradually getting more serious attention from critics are science fiction, children's and young adult fiction, and fantasy and historical fiction; perhaps in time it will also happen with romance and chick lit.
There remains, I think, an essential tension between literary and commercial or genre fiction, because we don't read them for quite the same reason. We want a literary novel to be a good book with fine prose and captivating ideas and characters, ideally one that will tell us something about the human condition, and we're prepared to work a bit to get our reward. However, we're quite happy for a commercial or genre novel to be a good bad book - provided it transports us effortlessly into the reading experience we expect.
With the influence of film and popular culture, there's more and more overlap between the categories to the point where even the most conscientious reader doesn't know or care how the book is labelled, as long as it's a good read.
As Orwell said: ''One can be amused or excited or even moved by a book that one's intellect simply refuses to take seriously.''
What's the best trashy book you've read lately?