The reason to go to this show? No, not for Ghostface Killah. No, not for Brother Ali. No, not for the live band, the Rhythm Roots Allstars. Yes, yes, yes for the father of modern rap, Rakim. He is, to put it in his words, the first rapper to "send a rhyme down the Nile." His moment in the history of hiphop was one of radical rupture, a break that inaugurated a new direction. Really, has hiphop moved beyond "Follow the Leader," a track Rakim made 20 years ago? (Showbox at the Market, 1426 First Ave, 8 pm, $32 adv/$35 DOS, all ages.) CHARLES MUDEDE