Love theater? Learn why

New book breaks down how Broadway builds its biggest smashes.

Jack Viertel changed my theater-going life, and he might change yours.

A few years ago, I had the extreme good fortune to sit in on a couple of the Broadway veteran’s lectures. Over the sessions — one in a classroom, and one in a living room, where he was accompanied by a singer and a pianist and a wine bar, which is really how these things ought to be done — he delivered terrific trivia, dry humor and a fascinating explanation of the architecture that holds up classic musicals.

I saved my recordings of those sessions and have listened to them repeatedly, always marveling at his insight. My only complaint was that I couldn’t share the experience with anyone who hadn’t been there. Now I can. “The Secret Life of the American Musical: How Broadway Shows Are Built” is a delightful, accessible guide to why your favorite productions work. It’s a little bit history, a little bit memoir, a little bit criticism and, for any theater fan, a whole lot of fun.

Musical theater, he tells us, is “the intersection of craftsmanship and the irrationally thrilling.”

The book explains the craftsmanship that goes into making those thrills.

As a man with stage credentials dating back generations (his grandfather built Broadway theaters, and Viertel has been hooked since he was 5 and saw Mary Martin in “Peter Pan”), it’s no surprise that he focuses on Golden Age mu- sicals, which he defines as the era from “Oklahoma!” in 1941 to “A Chorus Line” in 1975. But he’s no fuddy-duddy, and celebrates shows as contemporary as “Book of Mormon” and “Hamilton.”

His basic premise boils down to: Successful musicals share key ingredients that make them work. Failed musicals can be explained by their deviation from the pattern.

For example: Great shows share a great opening number that explains what the audience is in for. Classic case studies would be “Comedy Tonight,” which turned “A Funny Thing Happened on the Way to the Forum” from a flop into a hit, and “Tradition,” which caused a complete reworking of “Fiddler on the Roof.” (I can pause if you need a moment to finish humming.)

Next, a show needs a sympathetic character and a goal. Think of Little Orphan Annie, aching for her parents in “Maybe.” (“Won’t you please come get your baby ... maybe.”) Or Eliza Doolittle, longing for “a room somewhere, far away from the cold night air.”

Viertel explains why this matters: “The hero has to want something that’s hard to get, and go after it come what may.” A contrast between Eliza’s eternally compelling “My Fair Lady” with the same composers’ subsequent, less-enduring “Camelot” explains the power of having leads that the audience cares about: Eliza, a simple woman, longs for love and warmth; King Arthur and the “elegant, overbred and deeply entitled Guinevere” sing about how they want to be left alone, “and our instinct is to oblige them and let them go get a drink.”

Once the plot is in motion, audiences are ready for a big song and dance number — because “the energy in a theater has to move in both directions. The audience reacts to shifts in tone and mood and tempo by sending out its own burst of applause, laughter, and even tears. ... Theater is about engagement in the moment.”

Viertel can make these declarations — and many more, about love songs, showstoppers, star power and other key elements — because of his credentials. In addition to his family lineage, he’s worked as a theater critic and dramaturge, and is senior vice president at Broadway heavyweight Jujamycn Theaters. He played key roles in developing shows from “Angels in America” to “Smokey Joe’s Cafe.” So he has firsthand anecdotes about crucial decisions that made them work — or not.

Part of the book’s charm is that he’s as willing to discuss his brilliant moments — in “M. Butterfly,” his observations reshaped the climax — as his mistakes.

You can trust a writer who acknowledges that his “first dramaturigcal note” was delivered when he was 16 and seeing “Man of La Mancha” during tryouts. His unsolicited advice to the producer: Cut “The Impossible Dream.”

Is he saying there is a simple formula for Broadway success? Well, no, or there would never be a flop.

He reminds us that theater is more than just words, “it’s the word made flesh. Sometimes a light cue can make you cry. Sometimes an actor turning toward or away from another actor can tell more of the story than all the words a playwright could think up.”

His analysis is never academic, but in order to enjoy it, you’re going to need to know your show tunes. If you come across one you’re unfamiliar with, he provides a discography detailing every show he mentions, and a separate one for all the shows he leaves out. (If you’ve already spent your allowance on a theater subscription, I found almost all of them on Spotify.)

It would be easy to adore any book that gives us an excuse to blast a good tentpole number in the middle of a commute, but here is the true secret behind why I’m applauding Viertel: In a world where, in some quarters, Doritos ads pass as serious entertainment, “The Secret Life of the American Musical” makes us appreciate the art of making art. It’s more hard work than mystical, but when it comes together, it’s loverly indeed.