The funny thing about “A Funny Thing” is that the majority of the songs don’t work; in essence, they get in the way of things. These “things” are the machinations of a densely written farce by Burt Shevelove and Larry Gelbart. It terms of pace, and quantity of jokes-per-minute, this may be the best musical comedy libretto ever written.

Their idea was to take certain characters and plot contrivances from the ancient comedies of Plautus and pack them into a Vaudevillian farce. At almost any given moment, the dialogue sizzles with the oversized desires of its greedy characters. The main character is a slave who will do anything to get his freedom. His owner is a young man who will do anything to get the girl. The girl is a courtesan, owned by a procurer who will do just about anything for money. And he’s sold her to a strong and lustful soldier. And on and on. But the details aren’t as important as how humor springs forth when characters who desperately want someone are put into conflict. The complications pile up on each other at a rocket pace.

And then, disappointingly, we stop for a Stephen Sondheim song. It’s amazing, given the esteem Sondheim’s earned over the years, that in this first show for which he was composer as well as lyricist, the songs are the weakest element. The movie, wisely, cut all but a few. “Love, I Hear” is a song in which the young man we’ve already been introduced to introduces himself to us. There’s supposed to be charm to his naiveté but charm is not an element we’re positioned to enjoy. “Forum is clearly a Low Comedy evening. The jokes are on the bawdy side, and this song, which concludes by admitting it didn’t have much to say, is as unsexy as a song can get.

All members of the writing team must be on the same page. During the eight year gestation period, it seems the young Sondheim was unaware that low comedy was what the librettists were after. The show was in its pre-Broadway tryout, playing to very small audiences, when Jerome Robbins was brought in to have a look at it. He said nothing was wrong except the opening number, “Love Is in the Air.” “Love Is in the Air” is cute and sprightly, but that’s no way to introduce a down-and-dirty fast-paced comedy show. So, Sondheim was sent away to rewrite, and the new opener, “Comedy Tonight” set exactly the right tone. Once that was added, audiences loved what followed.