A song about a genre speaks volumes about the songwriter's agenda. There are tributes to forebears, such as Stevie Wonder's Sir Duke; cultural manifestos such as Mos Def's fierce restatement of rock's black roots in Rock 'N' Roll; angry jeremiads, like Nas's Hip Hop is Dead or Black Rebel Motorcycle Club's Whatever Happened to My Rock'n'Roll; and, in the case of sitcom actor Paul Nicholas's Reggae Like it Used to Be, homages so breathtakingly, unwittingly offensive they make your head explode. There's no ignoring our first two songs.

In 1979, Malcolm McLaren's art school classmate Robin Scott had a one-hit wonder with the wry, puckish Pop Muzik, which U2 would later adopt as the theme tune for their PopMart tour. During their formative months in Hamburg, the Beatles attacked Chuck Berry's Rock and Roll Music with such ferocity that it seemed to symbolise Britain's temporary takeover of this American artform. A special energy is generated when a genre announces its own arrival.

In the 1920s, self-appointed "originator of jazz" Jelly Roll Morton appropriated Joe "King" Oliver's Doctor Jazz as a celebration of both the music and his own good self. In 1986, Marshall Jefferson's Move Your Body decreed the house sound of Chicago so new and vital that it made all else redundant. A generation of clubbers embraced its credo of "house music all night long".

Reggae was well-established by 1976 but, perhaps in retaliation for Paul Nicholas, Bob Marley celebrated it afresh in Roots, Rock, Reggae. Some genres require justifying. Brooklyn rappers Stetsasonic responded to early criticisms of sampling with Talkin' All That Jazz's show-and-tell, backing up its lyrical defence of the sampler's art with an ingenious collage of borrowings from the likes of Lonnie Liston Smith and Donald Byrd.

Funkadelic, meanwhile, mocked 1970s genre divisions by asking (and answering) Who Says a Funk Band Can't Play Rock?! Away from the battle lines, Wilco wistfully recall a long-haired adolescence on Heavy Metal Drummer ("I miss the innocence I've known/Playing Kiss covers, beautiful and stoned"), while Lou Reed's own youthful, epiphanic discovery of rock radio inspires the Velvet Underground's elevating story of a girl whose "life was saved by rock'n'roll".

Finally, as if in response to all the above, Denim's Middle of the Road dismisses the entire classic-rock canon, moving from the deadpan slaughter of sacred cows towards a stirring call to chart your own path through musical history: a persuasive reminder that genre distinctions are merely a map, not a destination.