SPRINGFIELD, Ill. — Though it has often been noted how difficult it was to introduce polygamy into a puritanical society, it was even more difficult to move out of polygamy, the president of the Mormon History Association said Saturday night.

Kathryn M. Daynes, associate professor of history at BYU, delivered the presidential address for the association's 44th annual conference, which has been meeting in Springfield on the occasion of the Abraham Lincoln bicentennial. She is the outgoing head of the association, which selects a new president each year.

Addressing the topic "Render Unto Caesar: The Plight of 19th Century Polygamists," she applied to them the title of a 1960s popular song: "Breaking Up Is Hard to Do."

Daynes studied the cases of about 1,000 Mormons who were convicted in the latter 19th century of unlawful cohabitation in violation of the federal government's law cracking down on plural marriage in the Utah Territory.

Those convicted, after paying penalties or serving sentences, were required to promise to obey the law in the future. Most refused, but about 10 percent did promise, Daynes said.

"Even for those who said they would obey the law, it was a difficult decision to make," she said. "As I looked at this, what became so remarkable was how many of these families tried to stay together under difficult decisions."

She said she wanted to know something of their circumstances at the time they promised to obey the law, so she studied their situations. She looked at family and census records to see if they subsequently had children by their plural wives. About one-fifth did not obey the law, and of those, about two-thirds were prosecuted again.

Part of their problem was trying to figure out what the law meant, Daynes said.

She gave the example of Orson P. Arnold, the superintendent of the street railway in Salt Lake City. After his first offense, he was arrested again and charged with three counts. These stemmed in part from his visiting his plural wife to care for their sick child by taking him out for a carriage ride.

In an impassioned argument, the defense attorney said the prosecution asked "what no man with any instinct of manhood could do: to turn a deaf ear to the appeals of his innocent offspring," Daynes said.