Robert Ashley, an American composer who helped wrestle opera into the 20th century and in so doing broadened the genre in strange, unexpected ways, died on Monday at his home in Manhattan. He was 83.

The cause was liver disease, his wife, Mimi Johnson, said.

A prolific composer who first came to prominence in the 1960s, Mr. Ashley decided early to concentrate on opera. To him, though, the definition of opera was far different from what it had been for centuries, or even from what it was for many modern composers.

“I hate the word ‘opera,’ ” he told The New York Times in 1983. “I loathe and despise it because for us in the West it has only one, limited meaning.” He added, “The actual word means far more than our narrow usage of it.”

In Mr. Ashley’s hands, “opera” could take in spoken dialogue, chanting and even mumbling. His librettos, most of which he wrote, had little conventional plot. Unlike the gods, ghosts and noblemen that have long peopled grand opera, his characters were ordinary, even marginal.