Right from its formative stages amid the desolation of the 1970's Bronx - laid out in compelling detail by Chang's analysis of the almost psychotic carelessness of New York's city planners - the fundamental message of hip-hop has been of people making the best of what they have. If cuts in school music programmes stop you learning an instrument like the jazz and soul musicians of preceding generations, then why not develop your own parallel system of virtuosity making new sounds out of their old records? And if the only way to get hold of the equipment to do that is by looting turntables amid the chaos of the Big Apple's 1977 power-cut, well, maybe that's just the way it has to be.
For Afrika Bambaataa, the erstwhile leading light in the "Black Spades" street gang who became rap's "Promethean firestarter", it made perfect sense to draw inspiration for his peaceable Afrocentric vanguard The Zulu Nation from Michael Caine's swarming African adversaries in the film Zulu. It's this transformative impulse - the ability to take a profoundly insulting cinematic spectacle and reflect it back as a proud moment of black solidarity - that is at the heart of what might reasonably be called "hip-hop logic".
The colonial expansion of this mindset, outwards from the mean streets of New York's outer boroughs, is the central story of Can't Stop Won't Stop. And Chang is very good on the way hip-hop's fabled four elements - break-dancing, graffiti, rapping and dj-ing - got consolidated down to the last two.
One minute, the body-popping, spray-can- toting cultural ferment of early-Eighties New York was "reintegrating downtown clubs and vaulting society's outcasts into the art-world". The next, "Six man crews would drop to two. Fifteen minute party-rocking raps would become three minute for ready for radio singles. Hip-hop was refined like sugar." Sadly, Chang's acute awareness of what was lost as well as gained when hip-hop "went first all-city and then all-global" cannot stop (in fact it may even be responsible for) his book going totally off the rails at the point where rap has established itself as a mass medium with something to say.
Rather than heed the wise words of Public Enemy's Bill Stephney at a Howard University forum in 1987 - "woe be unto a community that has to rely on rappers for political leadership" - Chang gets horrendously tangled up in a doomed bid to establish his own brand of "hip-hop activist" as the only way forward for a form of music which has left such brown-rice pieties far behind. In a paroxysm of denial about the anti-art foundations of his own post-Adorno brand of Village Voice leftism, he overcompensates by striving vainly to fit the bulky body of the world's most popular music into a tiny ideological straitjacket borrowed from Louis Farrakhan's Nation of Islam.
The ultimate measure of a music book's worth is that it should sends you back to the records it has talked about. Can't Stop Won't Stop sends you back to the records it hasn't talked about. If you want to read a long and unbelievably self-indulgent trawl through the internal politics of US hip-hop magazine The Source, then this is the place to do it. But Biggie Smalls and Missy Elliott get just one mention apiece, and Eminem - white devil that he is - is excluded from history altogether.