The musical brought out some of the finest work from both: wit, bite and heartbreak in the libretto, and infectious melodies, cinematic underscoring and operatic sophistication in the score. Each decade of the story is indicated through musical signposts like spirituals and parlor songs in the 19th century, and an interpolation of George Gershwin’s “Rhapsody in Blue” in the 1920s.

Because music is so central to the plot, Kern and Hammerstein also wrote crucial diegetic songs. In the first act Julie, the show boat’s prima donna, sings “Can’t Help Lovin’ Dat Man,” which Queenie, the Black cook, interrupts by saying, “How come y’all know that song?” She has only heard “colored people” sing it before, she says, a revelation that presages Julie being unmasked as mixed race.

In Act II, years later, Magnolia, who is white and like a little sister to Julie, auditions with “Can’t Help” at a theater in Chicago. It turns out Julie is the star there, and she abruptly quits to make room for Magnolia. Magnolia then becomes a star, as if to embody the idea of Black culture being taken up (or taken over) by white entertainers, which is what happened with popular music in the early 20th century and continues to this day.

Kern signified the seriousness of this subject matter with a grand, dramatic A-minor chord in the Overture. Even more of a jolt, in the original Broadway run, was Hammerstein’s lyric for the opening chorus, in which audiences heard Black singers identify themselves with the most severe racial epithet. (In revivals, that word was changed to “darkies,” “colored folk” and, benignly, “we all.”)

Although there are offensive tropes in “Show Boat,” Hammerstein’s attitude was more nuanced, and progressive. The musical also contains advocacy on behalf of Queenie, for example, who is given a scene in which she is made to suffer, with seasoned cool, the indignity of a white man questioning where she got a brooch that Julie gave to her. And the musical’s biggest hit, “Ol’ Man River,” is reserved for Joe, the other principal Black character.