Slang divides opinion. "Squares" (first cited in the OED in 1901), or guardians of linguistic purity as they would have it, regard it as dangerous, vulgar, a debasement of language. In the other corner lurk overexcited "numpties" (1988) transported with delight by its youth, novelty, its anything-goes creativity.
Julie Coleman, professor of English at Leicester University, thinks they're both wrong. Slang is not a product "of poor breeding and poor taste" or a sign of limited vocabulary. "Puh-leeze!" (1931): as she points out, anyone who says "mega", "banging" or "wicked" could equally well use the Standard English "great", "fantastic" or "amazing". (And some of these words were once slang too, she reminds us.) Slang users are not particularly creative either: most of the subcultures renowned for their slang (teenagers, hippies, flappers) borrowed it from elsewhere. "Peeps", for friends, seems recent but was first used as early as 1847; "innit" is at least 50 years old; and most surprisingly, Coleman traces "nang" (excellent), to 1922, although other sources give it a far more recent provenance: slang etymology is tricky to pin down.
So what is the deal with slang? It's a way of identifying yourself as part of a group, and Coleman takes us on a journey through the real crucibles of slang – First World War trenches, prisons, 19th-century public schools – claustrophobic environments in which people collectively resisted oppression and expressed themselves. Only since the birth of the consumer society after the Second World War have youth and slang become so synonymous.
Slang's codes are notoriously hard to keep up with – "cool" has been cool and uncool again countless times – and by the time the secret passwords have been codified in a "proper work", they may be out of date. Even when an authority figure thinks they've cracked it, it ends badly. "An adult using youth slang is either ridiculous or creepy. What's key," notes Coleman, "is that you use it well in an appropriate context and in a way that achieves the result you want. Unfortunately, the judges of your success are applying ever-changing rules that no one will ever explain to you."
The Life of Slang is particularly acute on why slang works. It's a form of social grooming, allowing the saying of the same thing in a variety of ways, to help build relationships: "slang conveys a far more exuberant sense of admiration and humour than Standard English can". And her insight into how slang takes hold and spreads so rapidly is convincing: if you don't know the meaning of a slang word a peer uses you'd be a "muppet" (1989) to ask, and so you adopt it willingly.
Coleman relishes slang in all its chewy, vigorous glory, and gives a sociological insight – that context is key – which elevates it way above a dictionary of rude words. This book is "the cat's whiskers" (1920); or, if you're of a less delicate sensibility, "the dog's bollocks" (1949).