Are the characters' motivations pure? Are they sinister? Does it matter?
Now a new opera adaptation of the Danish director's film wrestles with the same questions, this time exploring them with music.
Composer Missy Mazzoli says she hesitated to create the work when librettist Royce Vavrek first proposed it.
"I thought it's such a brilliant film, so why mess with it?" she told AFP. "But the more I thought about it, the more I could hear a musical world that added a new dimension to the emotional landscape of the film."
"Breaking the Waves" premiered in September at Opera Philadelphia, where Mazzoli was composer-in-residence, and is being presented for a second time at Prototype, New York's annual festival of experimental opera that opened on Thursday.
Set in the Scottish Highlands, "Breaking the Waves" focuses on the psychologically troubled and sexually unfulfilled Bess, who marries Jan, a Nordic oil-rig worker.
After Jan is injured and sexually incapacitated, he encourages his wife to seek other lovers, scandalizing their Christian village as Bess pursues increasingly dubious trysts.
Von Trier is asking "what does it mean to be a good person when everybody in the community has different ideas of what it means to be good?" Mazzoli said.
"Particularly for a woman, this is a very familiar feeling," she said. "The line of behavior to walk on is very thin."
In the two decades since von Trier released his "Breaking the Waves," viewers have debated Jan's intentions. Does he want the best for Bess, or is he acting out of his own pleasure -- or even a desire to hurt her?
The late film critic Roger Ebert -- who ranked "Breaking the Waves" among the top 10 films of the 1990s -- concluded that Jan's reasons ultimately do not matter because Bess believes she needs to oblige his requests.
Mazzoli is firmly in one camp -- she thinks Jan's love is pure. While her opera preserves the ambiguity, she says her conclusion was important for the music as she opens the work with melodic love songs between Bess, portrayed by soprano Kiera Duffy, and Jan, performed by baritone John Moore.
"I tried to milk the happy moments in the opera because there are so few of them," Mazzoli said with a laugh.
She and Vavrek traveled to Scotland's Isle of Skye to record accents and slang and take in the scenery -- jutting rock formations, soaring cliffs and, of course, breaking waves, close to rolling meadows with lambs.
"The juxtaposition of that was striking and very inspiring," she said. "It struck me as a very loud landscape, even though it's a very quiet place."
She included Scottish touches by emulating the sound of bagpipes through oboe and strings -- although there are no actual bagpipes -- and song-and-response singing characteristic of Scottish church music.
First musical interpretation
Von Trier, a leader of the Dogme 95 cinema movement that frowns on special effects, eschewed music in "Breaking the Waves" except in brief passages.
"There is no underscoring telling you how to feel," Mazzoli said. "So there was this great opportunity to create a subtext through the music that illuminates the characters' psychology."
Von Trier gave his blessing to the project but was not involved, giving space to Mazzoli and Vavrek.
Known for his fear of flying, the film director will not see the opera in the United States, although Mazzoli said -- without revealing details -- that talks are underway for further productions worldwide.
Even among the opera's creators, there were disagreements about what drives Jan, she says.
"What makes the story so strong -- the ability to have many different interpretations," she said.
"Whether you love it or hate it, everybody comes out of this opera and this film and is talking about it."