In a rap world dominated by militant showboating and relentless self-aggrandizement, KRS-One, the main brain of Boogie Down Productions, is an influential and reliable voice of hip-hop reason. He stated his credo plainly last year on By All Means Necessary. "Boogie Down Productions is made up of teachers," he announced over the scratch 'n' slam of "My Philosophy." "The lecture is conducted from the mike to the speaker."

Ghetto Music: The Blueprint of Hip Hop is an extensive BDP lesson in black pride, intellectual achievement and the sorry state of most commercial rap. "Now in '89," KRS-One declares unequivocably in "Ghetto Music," "the purpose of a rhyme is to strengthen and uplift the mind." KRS-One is hardly above touting his own word power. He immediately throws down the gauntlet in the album's opening salvo, "The Style You Haven't Done Yet," over a taut funk-guitar motif. He nails a "soft silly low budget sucker" in "Breath Control," and in "The Blueprint" he hypes his own style of hip-hop soapboxing as "slammin' lyrics with beats unquestionable."

The stark rhythmic menace of the Boogie Down sound and KRS-One's no-nonsense verse are actually anomalies in mainstream rap, certainly compared with the Public Enemy school of shotgun sampling and clenched-fist rhetoric or Tone-Loc's style of more-casual funk. But Ghetto Music is about nothing if not getting straight to the point. The grooves are hard, with minimal but effective garnish – the subterranean dub-style rumble and Donald Duck vocal scratching on "Jack of Spades," the clarion gospel vocals of Pamela Scott in the heavy reggae hymn "Jah Rulez." "World Peace" is a notable exception, with horns, harmony vocals and a slow-boil rhythm that recalls the Seventies unity anthems of War. But it's an exception that really proves KRS-One's rule, that rap should look to its roots in ghetto culture for succor and inspiration instead of getting sucked up by crossover dreams.

Ironically, for someone who was instrumental in founding the Stop the Violence movement and recording the hit anthem "Self Destruction," KRS-One wastes the tough, extended reggae jams of "Bo! Bo! Bo!" on an unusually violent tale of a black youth on a cop-killing spree, supposedly acting in self-defense, like a Bronx variation on The Harder They Come. He states his case for black rage about police brutality with much less blood and much more logic on the short, angry "Who Protects Us From You?" "If I hit you, I'll be killed," he snaps. "If you hit me, I can sue."

KRS-One is actually a man of remarkable patience. By advocating higher learning and communal faith to rebuild the black spirit, he's embarked on the long road to change. But Ghetto Music shows that KRS-One has the mind and muscle to last the trip. "I don't drop science," he boasts in "Gimme, Dat (Woy)," "I teach it." Sign up for classes now. (RS 562)

DAVID FRICKE