Sometimes the hoopla is over one note; sometimes it’s over many, many more. When Manrico, the eponymous minstrel of Verdi’s “Il Trovatore,” fails to belt out a high C at the end of “Di quella pira,” all Italy rises up in arms. (Never mind that Verdi wrote no such note, and what is typically heard is actually a high B.) Same story when an Australian scholar blows the whistle on the published score of “Falstaff,” claiming to have discovered 27,000 departures from Verdi’s manuscript. Welcome to the madhouse of Italian opera, where tempers run high.

In “Divas and Scholars: Performing Italian Opera” (University Of Chicago Press, 704 pages, $35), Philip Gossett, the Robert W. Reneker Distinguished Service Professor in Music and the College at the University of Chicago, explores in depth the conflict between “tradition” and what the composer actually wrote. His declared perspective is that of “a fan, a musician, and a scholar.” Apart from very minor detours, he sticks to his specialty: the lyric theater of Rossini, Donizetti, Bellini, and Verdi.

Mr. Gossett knows his stuff. He is the general editor of monumental critical editions (in progress) of the operas of both Giuseppe Verdi and Gioacchino Rossini; among his countless decorations are a distinguished achievement award from the Andrew W. Mellon Foundation (worth $1.5 million) and the Cavaliere di Gran Croce, the highest civilian honor the Italian government bestows. Opera professionals — divas, scholars, conductors, directors, even mere music critics — know Mr. Gossett not only as a font of learning but also as a colleague of rare charm and generosity, though at need he can aim a poisoned dart. He recognizes few “moral obligations” in operatic performance. Yet he is scathing in cases of willful ignorance and knowing fraud. And while his gusto for archival research may suggest a pedant, he is as broad-minded and enlightened a pilot as any performer could wish for sailing some very treacherous waters. He reminds us, more than once, that Verdi’s barometer for success was the box office.

He takes no stand in principle against cuts, transpositions, interpolations, or the radical stagings also known as “Eurotrash” (though by no means all of them originate in Europe). Deep down, Mr. Gossett’s artistic philosophy is a plea for pragmatic decision-making that is historically informed. The universal command of Apollo’s oracle was: Know thyself. Mr. Gossett’s lays out the path to self-knowledge in his domain step by step: Know thy heritage. Know thy sources. Know thy history. Then make thy choices, and Godspeed. “A performance does not have the luxury of being indecisive.”

“Divas and Scholars” brings home how hard it can be to determine what the composer actually wrote. Many autograph sources are lost or unavailable, and interpreting the material is an art in itself. Authors make mistakes; they cross things out; they revise and correct. Even when the copy is clean, reading the notes requires a thorough knowledge of evolving conventions. Are two consecutive notes written at the same pitch meant to be sung at the same pitch? (The answer is often no.) And when a whole melody is repeated, is the singer meant to sing it the same way? (No again; a reprise in the period under discussion is a directive to embellish.) Really, an opera on the stage is much less like a play than like a Cecil B. DeMille spectacular, performed in sequence in the absence of the camera. Reproducing it just as it was the first time (or the last time) is beyond imagining. Personnel changes. Taste changes. Circumstances change. Like it or not, the job will always be to make it new.

For anyone aflame for the lyric theater of Mr. Gossett’s favored composers, “Divas and Scholars” will be a goldmine. But as any prospector knows, extracting treasure can be exhausting business.It is not encouraging, on the opening page of a main text running through page 532, to read a satire on the proclivities of vacationing Italians and to be told (on no authority) that the Mediterranean is less polluted than a decade ago. Later Mr. Gossett will comment on the quality of the licorice sold on the La Scala Web site (“horrid”). Chatty excrescences like these pop up constantly, and their charm wears thin.

Other, more pertinent matter becomes exasperating, too, as the author revisits it unnecessarily. (One minor instance of many: The history of the aria “Manca un foglio,” which is not by Rossini but was dropped into a revival of his “Barbiere di Siviglia” for the sake of a singer who could not negotiate “Un dottor della mia sorte.”) Detailed discussions of textual variants that might better have been laid out in tables bog down as narrative. On other occasions the author merely glances at a subject that deserves a longer look. And while he may deserve a certain credit for owning up to allegiances and pet peeves, his fawning on his bel canto paragon Marilyn Horne and his vendetta against the bel canto queen Beverly Sills (who once royally dissed him) grow equally tiresome. His concluding reminiscences of two Scandinavian productions constitute a 40+-page “coda” that feels wan and self-indulgent.

“I even delivered a boring paper,” Mr. Gossett confesses late in the game, I forget on what. But perhaps he is being uncharitable. Though there’s a shapely masterpiece imprisoned in his ungainly magnum opus, “Divas and Scholars” is seldom dull. Mr. Gossett writes graceful, often bracing prose. His common sense cuts through quantities of ill-reasoned argument; sometimes a well-placed “absurd” or “poppycock” is all he needs to prick a very big balloon. He initiates readers who need help into the mysteries of scordatura (special tuning), puntatura (personal adjustments to the vocal line), scene lunghe (scenes using the full depth of the stage), scene corte (scenes played before a curtain), and the aria di sorbetto (sung by a minor character while much of the public goes out for an ice-cream break). An incidental pleasure is his witty mastery of the scare quote and the square bracket.

In passing, he scatters nuggets of lore that open a window on truly prodigious stores of knowledge of matters “trivial and nontrivial,” if I may steal a phrase. Theaters in 19th-century Italy were no “temples of art,”Mr. Gossett writes, and briefly conjures up the scene. He mounts a persuasive defense for the much maligned figure of the librettist. He examines the symbiosis of stars and composers. He investigates the thorny problem of 19th-century translations of operas by Italian composers originally written in French. He discusses the special position of the brass band (often on loan from the local fire department).He quotes Verdi’s request for a description of Raphael’s fresco of Attila in the Vatican: Who could have imagined that for inspiration, the composer needed to know how the Hun wore his hair? Directors and designers who make audiences wait in the dark for a scene change are deservedly raked over the coals, on historical and aesthetic grounds. And there’s the odd flash of schadenfreude when misbehaving artists come to grief, as Samuel Ramey once did on an ostentatious, unwritten high F.

Without belaboring the point, Mr. Gossett establishes that all the disciplines he brings to bear indeed do relate in various ways to the textual editor’s lifelong quest. He and his scholarly peers (many of them his former students) do not seek to dictate to a diva. They seek to put at her fingertips the wherewithal to light the fires of her creativity. In the end, they want her to shine. The same goes for her male counterpart, the director, the designers, the conductor.

Inevitably, it’s an ambiguous proposition.As Mr. Gossett notes, documents are far from unequivocal: “They are the source of all truth, so to speak, but they are also the root of all uncertainty.” That’s the message, in a nutshell. From there on in, it’s all commentary, never-ending. The mind boggles. “Divas and Scholars” might have been much longer.

Mr. Gurewitsch last wrote for these pages about the original Mother Courage.