Violinist Daniel Hope and mezzo-soprano Anne Sofie von Otter perform from "Terezin - Refuge in Music." (Katja Schaefer/BADSK)

The Third Reich wanted to stamp out Judaism in music. The problem, writes the scholar Michael Haas in his new book “Forbidden Music: The Jewish Composers Banned by the Nazis,” was figuring out what that meant. Was Jewish music old, reactionary, tradition-bound, unable to be creative? Or was it new, offensive to the senses, avant-garde? The Nazis thought of themselves as forward-looking, but their artistic tastes were anything but progressive. They ended up sanctioning a lot of safe and since-forgotten music by party members, and tarring most of the rest with the brush of “degeneracy.”

Years have passed since the nightmare, but labeling music is still a thorny and controversial topic. Today, there are many and various ongoing efforts to return so-called “degenerate” music to the canon. What’s controversial is how to define this music. The term “Holocaust music” signals the general theme to people who might not know what “degenerate music” is. But in working to revive or remember art under such a sensational and clumsy rubric risks diminishing composers’ artistic achievement in favor of their historical importance: privileging artifact over art.

“By labeling certain works of art as ‘Holocaust music,’ ” wrote James Loeffler, an associate professor at the University of Virginia, in the online magazine Tablet earlier this month, “we risk creating a genre that turns the details of history and the complex meanings of music into one saccharine lesson in universalist tolerance. . . . The true heresy is to turn Jewish composers into shadow images defined only by their status as Hitler’s victims.”

For several decades, a number of musicians and musicologists have increasingly devoted themselves to the forgotten music of the Third Reich. The conductor James Conlon has started a foundation and led a number of operas from the early 20th century by composers who were later banned: Alexander Zemlinsky, Franz Schreker. The Italian pianist and musicologist Francesco Lotoro has made it his life’s work to track down every piece of music he can find that was written in a camp. The heirs of Franz Gál, who fled to the British Isles but never achieved the level of prominence there that he had enjoyed in Germany and Austria, simply want his music to be heard. Bret Werb, the music curator of the U.S. Holocaust Memorial Museum, focuses on popular songs: work songs, bitingly satirical cabaret numbers. “These songs from the ghettos and camps,” he says, “that is Holocaust music.”

And many performers, including the mezzo-soprano Anne Sofie von Otter, have at least dipped a toe into the repertoire from the bizarre “show camp” Terezin (or Theresienstadt), where some leading musicians were incarcerated and encouraged to create, in part to demonstrate to the world that the camps really weren’t so bad after all. (Many of them were later gassed at Auschwitz.)

So the music has been making its way in the world. But branding it is difficult. As a result, many audiencesfeel that what they are seeing represents a unique foray into a wholly forgotten realm.

Last month spotlighted two very different approaches to this repertory. One was the publication of Haas’s abovementioned book. Haas has been one of the leading voices in this field since he helped produce, in the 1980s and ’90s, the recording series “Entartete Musik” (“degenerate music”) on Decca, focusing on music that the Nazis proscribed. His book is dense and sometimes heavily written, with an occasional error (Liszt is said to be Wagner’s son-in-law, rather than his father-in-law) but it is also invaluable. Rather than focusing solely on the Third Reich, Haas contextualizes it. His subject is actually attitudes about Jews and Jewish composers in the German-speaking world from the early 19th century into the postwar years of the 1960s. For the confusion after the war was no less: composers whom the Nazis had called “degenerate” were often dismissed as “reactionary” by their own successors.

The other was a State Department event called “The Lost Music of the Holocaust,” which focused on the abovementioned collection of Francesco Lotoro. If Haas’s scope is broad, Lotoro’s is specific: he collects only music that was actually written in the camps. The collection numbers more than 4,000 pieces now, a few hundred of which Lotoro has recorded in the series “KZ Musik,” now up to 24 discs. (KZ, pronounced kah-tzett, is the German abbreviation for “Konzentrationslager,” or concentration camp.) Lotoro’s work, and his unquestioned zeal, have been attracting increasing media attention over the years: he is the subject of a French-language biography, and a documentary is in the works. An NPR profile of him earlier this year was one impetus for the State Department event, which included a world premiere performance — piano variations by a Polish prisoner named Leon Kaczmarek — of a piece from Lotoro’s collection.

This event was one of the things that Loeffler criticized in his Tablet article. His point, if made rather sweepingly, is that once you associate the term “Holocaust” with a musical work, people often suspend critical judgment. Lotoro’s collection clearly prioritizes the artifact as well as the art, presenting work by unknown composers side by side with work by significant ones.

“You simply don’t judge a piece of music by the fate of the composer,” says Charles Krauthammer, the political columnist and co-founder, with his wife, Robbie, of the series Pro Musica Hebraica, “even though you have an instinct to want to honor them because of their fate.”

Yet you could argue that Pro Musica Hebraica also operates along sociopolitical lines. The series does not present work proscribed by the Third Reich — “we have left that to others,” Krauthammer says — but its mission is to present music by Jewish composers, many of them not well-known. Any time that extra-musical concerns dictate concert programming — music by women composers, music by African American composers — you open up the question of whether it does the artists any favors to set them apart, or to categorize them by their religion, race or gender rather than by their art.

There’s also the question of why the work has been neglected in the first place. Haas, in his book, obliquely raises the question of how much of the “forgotten” music — going back to the 19th century and composers like Goldmark, Moscheles, Hiller and others — was neglected as a result of anti-Semitism, and how much as a natural consequence of changes in tastes and styles — or, to put it bluntly, because it wasn’t very good.

Conlon, the conductor, warned against this kind of thinking in a telephone interview last summer. “I don’t believe that every piece has to be a masterpiece,” he said. “It’s not about that. It’s about feeling the spirit of the time, the Zeitgeist.” But he also wants to correct the mind-set that “if you don’t know about it, it’s not good,” by giving forgotten works a second hearing. “History has been written with an enormous hole in it,” he says. “You have to revisit the subject. We should not sit back on the assumption that all the votes are in.”

Contrary to Loeffler’s implication, many artists and organizations shy away from the word “Holocaust” — in part because of a reluctance to capi­tal­ize on a current of what one might call voyeurism about the period.

But it’s also because, as both Haas and Lotoro’s work demonstrates, the term “Holocaust” is a misleading signifier for hard-to-categorize music. In Haas’s book, the actual Holocaust years occupy a single chapter.

Lotoro’s definitions have also evolved — most notably a few years ago, when someone sent him some music a German soldier had written in an Allied POW camp. “Francesco, who had converted to Judaism, had a long struggle with this,” says Dahlan Robert Foah, an American who is working with Lotoro to try to find a permanent home for his collection. But since Lotoro was collecting music by other non-Jewish camp inmates — Roma, Quaker, homosexual and others — he felt that logically he had to include this work, as well.

“When you talk about the Holocaust, a wall comes down,” says Foah. “What we’re trying to do is find a tunnel under that wall . . . start a discussion of the creativity that’s involved.” Whatever the terminology, that goal, at least, is shared by everyone else.