“Saw Lady in the Dark tonight, & loved it … ,” Bernstein wrote to Copland in December of 1940. “It is, as you say, slick—over-slick—but I’m no critic, being an analysand(!).” Weill's “musical play in two acts” adopted an experimental form that was novel for Broadway at the time. Lady in the Dark was also the first musical drama based on psychoanalysis, influencing not just a range of Broadway shows about psychotherapy but, through the Paramount film version, American cinema. The score absorbs elements from Zeitoper, operetta and musical comedy, veering with at times filmic cuts between dream sequences and the everyday life of the female protagonist, the magazine editor Liza Elliott, as she struggles to reconcile her professional and private personas in therapy sessions with Dr. Brooks.

Liza's three dreams are structured by dance rhythms (rhumba for the “Glamour Dream,” bolero for the “Wedding Dream” and march for the “Circus Dream”) that create formal cohesiveness while also commenting ironically on the drama. In what Bernstein may have perceived as “slick,” Weill also manages to create transitions through the sparsest of instrumentation. Both Copland and Bruno Walter were reportedly astonished at the shifts from realistic scenes to dreams upon discovering that a single clarinet underscores Liza when she hums the tune from the song “My Ship” at the opening of the “Glamour Dream.”

Over the course of therapy, Liza hums fragments until she recalls the number in its entirety. As mcclung writes, song itself becomes a meta-dramatic thread: “when Liza is finally able to remember a childhood song and the traumatic events tied to it, her psychosis comes to light, and her complicated love life straightens itself out.” The recovered memory coincides with a path to emotional stability and her realization that she does not want to marry the magazine publisher Kendall Nesbitt, with whom she has been having an affair, or the movie star Randy Curtis, but rather the advertising manager Charley Johnson.

Weill labored to adapt his style to the idiom of Broadway. With “My Ship” providing a germ for the entire score, mcclung considers Lady in the Dark the first work in which the composer “made popular American song form his primary vehicle for vocal composition.” The number evolved from a highly chromatic “valse lente” to a rocking duple-meter rhythm, going through five different drafts until Weill was satisfied.