Pop forms cycle through phases: First the hard, saw-toothed edge is to the forefront, then it gets cushioned in soft velour (often woven out of violins and choirs), then that covering gets ripped away and you feel the rough, brittle shell, then it breaks open and the soft gooey centre spills out. Rinse, repeat. It's obvious enough when you look back over the history of country music or rock, both of which seem to be heading back to the tougher side now.

In both rock and country, the axiom (right or wrong) has been that the rough stuff is the source of innovation: Rawness is truth, violence is strength, stripped-down is honest. When things get too squishy, the most demanding part of the audience starts to squirm and, as legend has it, the young punks and outlaws provide a reality check.

That same set of reflexive values has been superimposed on hip-hop in the past 20 years: "Keeping it real" means keeping it on "street" level, and the streets, don't you know, are mean and murderous. It's long been a debate how much of that image grows out of rap's roots in ghetto culture, which are anything but mythological, and how much of it has to do with the music industry's desire to play on white suburban fantasies of gang machismo.

Yet hip-hop has also provided us the first chance since the 1950s to see a more or less new branch of truly popular music emerge and define itself. Like rock, it's opened a cultural space different than anything that came before, and gone on to conquer the world. I don't know what Thomas Kuhn, the scientist-philosopher who came up with the term "paradigm shift," would say, but it seems to suit human nature that we are still trying to understand rap in rock terms, using the slogans of one revolution to interpret the next. After all, most mainstream critics (this one included) first warped their faculties on the rock narcotic.

But the actual development of rap scrambles the signal. Ever since radio and TV got over their early skittishness about baggy pants and baseball caps, when Public Enemy and then NWA became stars (around 1989, which you might call rap's 1956), commercial hip-hop has been dominated by hard men who wore the colours of thugs and pimps. With a few, undeniably significant exceptions such as the successes of De La Soul and Lauryn Hill, the soft, sensitive side of rap has thrived mostly in the underground, where the return to "old-school" values has been the most consistent rallying cry.

Nowhere is that more true than in the Bay Area around San Francisco, where wave after wave of thoughtful hip-hop artists have arisen to denounce or mock the materialism and nastiness of their more successful peers, to make a more "organic" sound or preach a more "conscious" message. The result is usually a flurry of newspaper articles about how there's more to hip-hop than ego and "bling-bling," as if that were news. And then a slow fade that leaves behind a stale odour of disappointment, a list of debts from the band to whatever major record company signed them, and more gangstas and tycoons bragging up the airwaves.

Bay Area duo Blackalicious has been around in one incarnation or another for over a decade and has seen all the snares. And judging by the sound of Blazing Arrow, the group's second full-length CD and its first co-released with a major label, its solution to the confusion over what makes for radical hip-hop is to ignore it. (Blackalicious plays the Opera House in Toronto on Saturday, 735 Queen St. East, $22.50.)

The credibility of rapper Gift of Gab and producer Chief Xcel is impeccable, despite the very middle-class, university-educated tone of their lyrics. Their collaboration began in high school and carried on into Solesides, the hugely influential early-nineties collective that also included DJ Shadow, Latryx, Lyrics Born and Lateef the Truth Speaker, who've all gone on to different degrees of acclaim. Solesides became the Quannum label, which put out the Blackalicious disc Nia to much applause in 2000; it featured Xcel's polyglot jazz-soul sounds and Gab's silver-tongued spiritual reflections after years of struggling with alcoholism. It went into the ear as ambrosia but hit the gut more like thick syrup.

Blazing Arrow has its moments of dull, eat-right-be-nice vegan proselytizing too, but they're just brushstrokes on a much bigger canvas that is as rich in technique, texture and temperament as a classic album by Prince or Funkadelic or, more recently, Outkast. On most rap discs, guest cameos seem like gimmicks or time fillers, but Blackalicious invites others aboard simply because there's a party going on and it's the natural thing to do. An almost eerie jazz vocal by seventies rap pioneer Gil Scott-Heron, a neo-soul chorus from Jaguar Wright, the smooth sensuality of Ben Harper and a jack-rabbit-meets-jackhammer invocation by ex-Rage Against the Machine frontman Zack de la Rocha all blend easily into a constantly paradigm-shifting sonic collage.

Meanwhile, DJ Shadow lends the unerring precision heard on his recent Private Press album to Xcel's already virtuosic mixes, and even a sample of Harry Nilsson's early-seventies kids' tune Me and My Arrow seems at home as a chorus on the title track. Gab's wordsmithery may get overrated by the indie-rap faithful now and then, but his lazier recitations are often belied by a switch into the slippery-tongued cadences of an auctioneer on the just-because-I-can showpiece Chemical Calisthenics (in which he riffs off the periodic table at about the speed of light) or the politically deft Paragraph President.

There's no doubt of the independent spirit here, but the righteousness of the self-sufficient small-label rap crowd is no longer the whole point. When there's as much musical experimentation in the background of many pop hits as there is on a sonic juggernaut like El-P's grand new Fantastic Damage disc, Blackalicious seems to figure the underground might just as well muddle up the hard and the soft in search of serious fun. If a hit comes along, they're not complaining, but they're not holding out a gilted beggar's bowl either.

It's a new sound in the old ceremony, not trying to change the musical world so much as finding a way to step in and out and around it, and it insists that there's a lot more to the "street" than usually meets the ear. Or, to borrow another phrase from the last revolution, that there's more than one cure for the summertime blues.
cwilson@globeandmail.ca