Ronald Dworkin, an innovative legal thinker who developed a novel interpretation of the moral underpinnings of the Constitution and who became respected in liberal circles for his writings on law, politics and hotly debated public issues, died Feb. 14 in London. He was 81 and had leukemia.

New York University, where Mr. Dworkin was a law professor, announced his death.

Mr. Dworkin, who also taught for many years at the University of Oxford in Britain, went against a century of legal thinking — including the theories of his two most important mentors — to develop a new concept of jurisprudence based on society’s widely shared notions of morality.

His idea of “law as integrity” held that jurists should interpret legal cases through a consistent set of moral principles. In other words, law and morality were inextricably linked, which was a subtle twist in legal thinking. Mr. Dworkin’s theories gained a wide following, particularly among social liberals.

“For many, Dworkin was something of a legal prophet who tried to invest legal interpretation with a sense of moral reasoning,” Jonathan Turley, a law professor at George Washington University, said Thursday. “His writings offered a new and transcendent view of the law — a view that will influence legal reasoning for generations.”

This is an undated file photo of Ronald Dworkin provided by New York University. Dworkin, the American philosopher and constitutional law expert best known for articulating the principle that the most important virtue the law can display is integrity, has died. (Leo Sorel/AP)

In one of his landmark books, “Taking Rights Seriously” (1978), Mr. Dworkin rejected the two prevailing theories that had dominated legal thinking in the United States and Britain for most of the century: legal positivism and utilitarianism.

Legal positivism maintained that individuals possessed only those rights granted to them through political decisions or long-standing social practices. Utilitarianism suggested that the law should uphold the principle of providing the greatest good for the greatest number of people. By that theory, Mr. Dworkin pointed out, the rights of a minority would always be subject to the will of the majority.

The theories had been espoused by H.L.A. Hart, Mr. Dworkin’s onetime professor at Oxford, and by Learned Hand, a federal judge in New York whom Mr. Dworkin served as a law clerk. Nonetheless, he challenged their ideas by charting a new way of thinking about legal principles.

In other books, such as “Law’s Empire” (1986) and “Freedom’s Law” (1996), Mr. Dworkin explored concepts of jurisprudence and the Constitution, which he saw as a living document built around abstract moral principles open to changing interpretations throughout history.

“He viewed the discussions by the framers as a moral dialogue about the role of government in the lives of human beings,” Turley said. “Dworkin offered a distinctly new and provocative view of what the framers were talking about. That’s what made him so remarkable.”

Mr. Dworkin applied his notions to a series of controversial issues, including abortion, affirmative action, free speech, campaign finance, terrorism, civil liberties and physician-assisted suicide. He became known as a “public intellectual,” writing for the New York Review of Books and lecturing at universities throughout the United States.

He supported affirmative action programs for minorities because, as he told Time magazine in 1977, “ ‘the right to be treated as an equal’ does not always mean ‘the right to equal treatment.’ ”

In his 1993 book, “Life’s Dominion,” Mr. Dworkin argued that opposing views on abortion were, in effect, articles of religious faith. By that reasoning, any judicial effort to overturn Roe v. Wade, the 1973 U.S. Supreme Court decision that effectively legalized abortion, would be equivalent to establishing a state-sanctioned religion. He believed that tolerance for opposing views of abortion should become a part of a pluralistic society, the same as tolerating different religions. Mr. Dworkin’s writings made him anathema to many conservative legal scholars, most notably Robert H. Bork, the former federal judge who once taught alongside Mr. Dworkin at Yale Law School.

“Dworkin writes with great complexity,” Bork wrote in his 1997 book “The Tempting of America,” “but, in the end, always discovers that the moral philosophy appropriate to the Constitution produces the results that a liberal moral relativist prefers.”

Ronald Myles Dworkin was born in Worcester, Mass., on Dec. 11, 1931, and completed high school in Providence, R.I. He graduated from Harvard University in 1953, then studied law at Oxford two years on a Rhodes scholarship. After receiving his law degree from Harvard in 1957, he worked as a law clerk for Hand.

Mr. Dworkin practiced law in New York for a few years, then taught at Yale from 1962 to 1968. He was at Oxford from 1968 to 1998 and, beginning in 1975, had a joint professorship at NYU, where he led a weekly symposium in which he exchanged ideas with other legal theorists, philosophers and scholars.

Mr. Dworkin’s wife, Betsy Ross Dworkin, died in 2000 after 41 years of marriage. He was romantically linked with Irene Semler Brendel, who was previously married to classical pianist Alfred Brendel. Other survivors include twin children from his marriage, Anthony Dworkin and Jennifer Dworkin, and two grandchildren.

Known as an eloquent speaker and sparkling writer, Mr. Dworkin touched on deeply philosophical subjects in some of his books about the law.

“Death’s central horror is oblivion — the terrifying, absolute dying of the light,” he wrote in “Life’s Dominion.”

But he also liked to recall the time he introduced his future wife to Hand, often called the greatest U.S. judge never to serve on the Supreme Court. The 85-year-old jurist invited the young couple into his house, mixed dry martinis and talked for two hours about art history, politics and education.

Mr. Dworkin’s future wife was charmed by the elderly judge.

“If I see more of you,” she asked Mr. Dworkin, “do I get to see more of him?”