He's the sphinx of American musical theatre; at 79, a kind of relic of the heroic past. He was mentored by Oscar Hammerstein; knew and worked with Richard Rodgers, Leonard Bernstein, and Jerome Robbins; penned 'a nervous breakdown' for Ethel Merman, a Broadway break-out for Chita Rivera, and unforgettable roles for Elaine Stritch and Angela Lansbury. In the process, he re-invented the form of musical theatre again and again. And again. And again.

"He," of course, is Stephen Sondheim, one of the few acknowledged geniuses on the planet, and a man whose theatrical career knows few parallels. He is either the lyricist or composer (or both) of five of the best musicals ever made: West Side Story, Gypsy, Company, Follies, and Sweeney Todd, and the creator of several more that are nearly as great. He owns an Oscar, several Grammys, a Pulitzer, and nine Tonys. His achievement is poignant in only one respect: once hailed as a harbinger of the future, he is now understood to be the last of his kind; not the prophet of a new age, but the apotheosis of an old one.

And he came to Boston last weekend, in the company of former New York Times drama critic Frank Rich, as part of the Celebrity Series fall season. Needless to say, it was wonderful to simply see him in the flesh; Sondheim looked spry, and his voice and manner could have been those of a man twenty years younger. Certainly his wit was as sharp and focused as ever, and it was easy to imagine that whatever the eventual fate of Road Show (the lengthily-developed project which has yet to see Broadway), Sondheim could, perhaps, still have another great musical in him - whatever doubts he himself may have expressed about that!

Still, over the course of the conversation, I'm afraid the sphinx kept all his secrets (something that Sondheim has always been famous for doing). Not that anyone expects this kind of celebrity ritual to turn into a confession. Still, Sondheim's history, both artistic and personal, is so rich that I think Rich could have mined a few more insights - or at least heretofore-unknown quotes - than he did; a perusal of just Sondheim's Wikipedia entry is far more fascinating than their repartee turned out to be (the young Sondheim in a professional portrait, above). And the conversation often wandered into odd critical pronouncements that were about as eccentric as you might expect of Stephen Sondheim; is Sweeney Todd really the "only film musical designed for film"?? Is Ravel really the source of Broadway's musical style??

Okay, so Sondheim's not much of a critic, and perhaps his and Rich's act has become something of a routine (they've taken it on the road before). My chief problem with the program was that the Harvard alum made the cardinal mistake - so tempting to any interviewer, I admit - of making the conversation mostly about his own relationship with the interviewee. It's interesting, perhaps, for Rich to point out how early he himself perceived Sondheim's greatness (at tryouts of Forum, and later Company and Follies), while the Broadway hoi polloi couldn't see the light - for some reason, the bourgeoisie always adores hearing in retrospect how artistically blind it is. I think it would have been far more interesting, however, if Rich had managed to tease out of Sondheim some sense of how he achieves his mysterious synthesis of lyric and melody, or what really goes into "putting it together" (beyond the well-known tale of the addition of "Comedy Tonight" and "Being Alive" to Forum and Company, respectively). For like many shows, Sondheim's masterpieces were often thrashed out in previews - a process which doesn't really exist anymore (it's been replaced by "development," which is hardly the same thing). And louring over any conversation with Sondheim at this point is the long gestation (and many false starts) of Wise Guys/Bounce/Road Show, which itself is easily read as a proxy for the twilight of the musical itself. The form, to be blunt, is probably on its death bed, whatever people pretend about Rent or Spring Awakening. So how does the master feel about that, and does he have any particular prescriptions for the Fabulous Invalid?

We left the conversation (which ended abruptly, after only two pre-submitted questions from the crowd) without ever knowing - and indeed, without knowing much of anything that hasn't often been said and cited about Sondheim before. Still, for a few moments, we breathed the same air as the Sphinx, and for many, that may have been enough.