Supreme Court Justice Antonin Scalia may be the most polarizing figure in American law. Conservatives see him as an icon faithful to the Constitution. Liberals see him as an ogre on the wrong side of history.

Last week, liberals asked a pointed question: How can Scalia have the temerity to express constitutional doubts about affirmative-action programs on Monday, and to vote to invalidate the Voting Rights Act on Tuesday — then piously argue on Wednesday that the Supreme Court should defer to Congress and uphold the Defense of Marriage Act?

It's a legitimate question, and whether or not it has a good answer, Scalia remains poorly understood by his admirers and his critics alike.

Perhaps his central goal has been to promote the rule of law, which (as he contended in an important essay in 1989) is "a law of rules." He seeks to increase predictability. He favors general rules, not case-by-case judgments.

In his view, such rules simplify life for ordinary people and the legal system. They also reduce the danger that political preferences will dominate judicial decisions.

Because of his commitment to predictability and democratic self-government, Scalia insists that laws must be interpreted in accordance with their ordinary public meaning — the meaning that their words had in the nation or community that enacted them. Of course, Scalia is aware that words can be ambiguous; in such cases, he is willing to defer to the interpretation of the executive branch (whether the president is a Democrat or a Republican). What he insists on is that the ordinary meaning governs if judges can identify it.

That commitment isn't connected with any political ideology; it can lead to liberal results. For example, Scalia recently wrote an important voting-rights opinion (over vigorous dissents from Justices Clarence Thomas and Samuel Alito), ruling that the language of the National Voter Registration Act bans Arizona from requiring voters to provide documentary evidence of U.S. citizenship.

As an "originalist," Scalia believes that provisions of the Constitution mean what they meant at the time that they were ratified. He thinks that originalism increases predictability and ensures the sovereignty of We the People. The meaning of constitutional provisions is a question of history, not morality.

With respect to the Defense of Marriage Act, originalism (as Scalia understands it) leads to a clear conclusion: Congress may refuse to recognize same-sex marriages. In his words, "the Constitution neither requires nor forbids our society to approve of same-sex marriage, much as it neither requires nor forbids us to approve of no-fault divorce, polygamy, or the consumption of alcohol."

Is this position incompatible with his conclusion that affirmative-action programs violate the Equal Protection Clause? Maybe not. In his view, the constitutional requirement of "equal protection," understood in its original public meaning, forbids all forms of racial discrimination.

Chief Justice John Roberts wrote the court's Voting Rights Act opinion, but Scalia probably believes something like this: If the 15th Amendment is to be interpreted in accordance with its original meaning, Congress's power to enforce that amendment "by appropriate legislation" doesn't allow lawmakers to continue to use an outdated preclearance formula that covers states on the basis of practices that were eradicated long ago.

There are formidable objections to originalism, which is hard to square with some widely accepted constitutional practices (including the prohibition on racial discrimination by the federal government and on sex discrimination in general). Affirmative action may well be consistent with the original understanding of the 14th Amendment. It remains puzzling that Scalia has yet to discuss the historical materials, which create serious problems for his insistence on colorblindness.

By all accounts, Scalia is a wonderful colleague, but some of his opinions test the boundaries of civility. One of the most vivid writers in the court's history, he knows how to deliver a punch. Sometimes he seems to think that people who don't see things his way aren't merely in error but are also foolish, unacceptably political, even lawless.

Those who disagree with Scalia are entitled to object to his votes and tone. At the same time, they should understand that his broadest commitment is to the rule of law. And they should respect his efforts to develop an approach to interpretation that is compatible with it.

Cass R. Sunstein is the Robert Walmsley University Professor at Harvard Law School and the former administrator of the White House Office of Information and Regulatory Affairs.