I somehow miss Margo's post in the beginning of this thread. Contrary to what she (and Sondheim) may say, Porgy & Bess in its definitive and intended form is an opera, not a musical or an opera-musical hybrid. Here are a few things Gershwin himself had to say about the work:
"If I am successful it will resemble a combination of the drama and romance of Carmen and the beauty of Meistersinger."
I am very familiar with both Carmen and Meistersinger. Like Carmen, Porgy and Bess has beautiful songs that are an integral part of its musical makeup. The comparisons to Meistersinger are even stronger. The large choral ensembles and dramatic scenes, the effective use of leitmotifs, the Wagnerian scope and difficulty of its principal roles, and the fight-scene fugue owe much to Wagner's work. Above all, however, there is a similar feeling of community that links Catfish Row with Nuremburg. Clearly Porgy and Bess was influenced and modeled after these two great operatic works.
Here's what Gershwin had to say about the songs in the work:
"It is true that I have written songs for Porgy and Bess. I am not ashamed of writing songs at any time so long as they are good songs. In Porgy and Bess I realized that I was writing an opera for the theater and without songs it could be neither of the theater nor entertaining from my viewpoint.” He further went on to say, “But the songs are entirely within the operatic tradition. Many of the most successful operas of the past have had songs. Nearly all of Verdi’s operas contain what are known as ‘song hits’. Carmen is almost a collection of song hits. Of course, the songs in Porgy and Bess are only a part of the whole…I have used symphonic music to unify entire scenes.”
There you have it…from the mouth of the composer – he intended Porgy to performed as composed - as an opera, and it is a grand opera, not a musical, operetta, or hybrid.
"What the hell happened to you? You look like a Make-A-Wish Kid. You know, I just knew you were gonna bring shame on this new family of ours, and it just figures you had to go make yourself over into some heroin-shootin skate board chic on the only day E! could interview you!" - Cherry Cherry, on her daughter Mary Cherry