 For help in figuring out what to make of Tibbett's Porgy, I conferred with John McWhorter, whose New York Times columns regularly deal with culture and race, and also with George Shirley, who was the first black tenor to sing leading roles at the Met. Here's what McWhorter had to say about hearing Lawrence Tibbett sing Oh Bess, Oh Where's My Bess and five other numbers from Porgy and Bess.