Mary Daly - who emerged as a major voice in the women's movement with her first book, "The Church and the Second Sex," published in 1968, and "Beyond God the Father: Toward a Philosophy of Women's Liberation," which appeared five years later - died last Sunday in a Massachusetts nursing home. She was 81.

Her writings were viewed, then and now, as all the more significant because she wrote and taught at a Jesuit university.

"She was a great trained philosopher, theologian and poet, and she used all of those tools to demolish patriarchy - or any idea that domination is natural - in its most defended place, which is religion," said Gloria Steinem.

Dr. Daly taught at Boston College for more than 30 years, but her relationship with the institution grew tempestuous as she insisted that only women could take her classes.

Sister Joan Chittister, feminist author and member of the Benedictine Sisters of Erie, Pa., said Dr. Daly turned standard theological concepts upside down.

"Mary played with language in such a way that you simply had to stop and think," Chittister said. "You couldn't use old words in the old ways."

"Ever since childhood, I have been honing my skills for living the life of a Radical Feminist Pirate and cultivating the Courage to Sin," she wrote in the opening of "Sin Big," a 1996 autobiographical article for the New Yorker magazine. "The word 'sin' is derived from the Indo-European root 'es-,' meaning 'to be.' When I discovered this etymology, I intuitively understood that for a woman trapped in patriarchy, which is the religion of the entire planet, 'to be' in the fullest sense is 'to sin.' "

Dr. Daly's career at Boston College, where she joined the theology faculty in 1966, ultimately ended over what administrators saw as her sin of exclusivity. After the college went co-ed in the early 1970s, she allowed only women to take her classes, teaching a few men privately over the years.

The dispute spilled into the courts in the late 1990s when a male student hired a lawyer after Dr. Daly barred him from her class. The college tried to force her into retirement, and she sued, citing breach of contract.

She and the college reached a settlement in 2001 and, at 72, she agreed to retire.

Those who knew Dr. Daly and her work say the dispute did not diminish her contributions.

"I think she was a central figure for the feminist movement in the 20th century and hopefully beyond," said Robin Morgan, who edited "Sisterhood Is Powerful: An Anthology of Writing From the Women's Liberation Movement." "She redefined the parameters of philosophy."