It is certainly true that book writers do more than just provide the spoken dialogue, but I don't think it's true that they "usually" provide the "song titles", as asserted above. They may very well, however, suggest places for songs and even summaries of the content of lyrics, depending on how the book is written. They also usually provide the plot, define the characters, etc. Elmer Rice is credited with the book for STREET SCENE, even though the work is nearly through-sung; the same may be said of Hugh Wheeler for SWEENEY TODD.
But book is NOT "slang for libretto". The term libretto refers to book and lyrics; the term basically means "the words" as befits its literal translation: "little book". If there are two meanings to the term "book of a musical" (and there are) they are these: the narrow meaning refers to spoken dialogue as opposed to sung; the broader meaning refers to the entire structure of the show. In the latter case, all the writers and the composer basically share responsibility for the "book".
If you read books on collaborations such as Sondheim's with Hugh Wheeler or John Weidman or even Arthur Laurents, it's more that the title and subject of a song are suggested by dialogue found in the book. The best songwriters admit they "steal" from the book writer all the time. That's just one reason writing the book is a rather thankless job. The other is that everybody credits the score for a success and blames the book for a failure.
P.S. I don't know what production of RAGTIME had "a lot of dancing". It certainly wasn't the version (LA) I saw. It would be more accurate to say there was a lot of strolling. This is not to say Ahrens didn't say otherwise, but if so, I think she was engaged in hyperbole.
Updated On: 1/17/16 at 10:31 PM