Mr. Rosen’s encyclopedic knowledge made itself felt on and off the stage for more than five decades. His concert-hall repertory extended from Mozart to Debussy to Elliott Carter, making it so hard to pin him down that his recording label, CBS, eventually gave up on his contract. His versatility served him admirably as a music scholar.
Having taken up writing in a kind of self-defense — “to begin with I wrote just to keep nonsense off my record sleeves,” he once said — he won a National Book Award for his first major book, “The Classical Style” (1972).
The book was a thoughtful, erudite and soundly argued study of the music of the three principal composers of the Classical period: Haydn, Mozart and Beethoven. Hailed as an instant classic, “The Classical Style” remains the definitive book on the music of that era — which spanned the late 18th and early 19th centuries — which did so much to define the Western canon. Filled with examples of notated music, the book was at times a demanding read for a lay audience.
“The Classical Style” launched a writing career that extended through several other volumes. Mr. Rosen also became a prodigious contributor to the New York Review of Books, writing about classical composers but also subjects including philosopher Isaiah Berlin, the cookbook writer Elizabeth David, Parisian art exhibitions and the Restoration-era English playwright and poet William Congreve.
In a 1977 New York Times interview, Mr. Rosen called writing his hobby.
“At the piano, if you practice 10 hours a day, then you have no time to write,” he said. “I really can’t practice more than about four to five. I can play the piano for eight to 10 hours a day, but I can’t practice for that long. So I have to do something with my time.”
Charles Welles Rosen was born in New York City on May 5, 1927. As a child, he attended the prestigious Juilliard music school in Manhattan and then studied with the pianist Moriz Rosenthal, who had been a pupil of the 19th-century Hungarian pianist and composer Franz Liszt.
The connection to Liszt put Mr. Rosen in a direct line with the grand romantic tradition that was later to become the subject of one of his books.
Rosenthal was no slouch at the kind of incisive one-line put-down that Mr. Rosen was to incorporate into his writings. He also connected his young student with the musical and intellectual life of New York.
When Mr. Rosen matriculated at Princeton University, he said in interviews, he already knew the whole music department and what it might have to teach him. Instead, he majored in French literature, eventually earning a doctorate from Princeton in 1951. He then won a Fulbright scholarship, going to Paris to study 15th-century musical manuscripts.
Meanwhile, his piano career continued with high-profile performances at Town Hall in New York and the release of his first recordings.