What makes it great? When it comes to sex, I can tell you. But when it comes to music — well, I was trained as a concert pianist, and if anybody were to ask, “Hey, what makes that piece you’re playing great?” ... I’m not sure I could say. Some pieces are great because they’re so complex, or so full of the unexpected. Others are brilliant in their simplicity. Still others could qualify because they’re so boldly original, or so obnoxious in their originality, that they force you to react to them, one way or another. But as to the precise elements that distinguish a master work from a mediocre one — well, I’ll leave that to the expert, Robert Kapilow. Dubbed the “Pied Piper of Music” and “classical music’s greatest evangelist,” and hailed as the successor to Leonard Bernstein, Kapilow — whom you’ve probably heard on National Public Radio — has achieved fame as both a pianist and composer of note (Green Eggs and Ham) and a music historian for the masses. His fascinating discussion series “What Makes It Great?” has turned the classically clueless across the country into avid enthusiasts; the baby-faced boy wonder has the rare ability to coax an untrained ear to appreciate the complexities of a Mozart aria or the messages in a Schubert quintet in the course of a couple of hours. His philosophy is simple: Involve the listener. “Music is not a passive thing,” he insists. “It should be like an engaged conversation.” And with his bubbly, rapid-fire stand-up-comedy approach, one can’t help but enter into the fun. This week, Kapilow and his guest artists — members of the Pacifica Quartet — will show us what makes Shostakovich’s Quartet No. 8 in C minor great with a three-part program that includes a discussion of the composer and the work, a performance of the quartet, and a “spirited and eclectic” Q&A with you, the audience. Cerritos Center for the Performing Arts, 12700 Center Court Dr., Cerritos; Wed., Sept. 17, 7 p.m.; $25. (562) 467-8818.