In law school, I took a yearlong administrative law course from Stephen Breyer. Many people find "ad law," the law of agencies and government regulation, fairly dull. But Justice Breyer, who was not yet on the Supreme Court, could barely contain his enthusiasm. He talked animatedly, week after week, about subjects like Congress's decision to mandate air bags in new cars. At the end of every class, we made a point of checking how much chalk there was on his suit, since he tended to back into the blackboard in his excitement over topics like "agency nonacquiescence."

Early in his career, Justice Breyer was counsel to the Senate Judiciary Committee, where he worked on the federal criminal code, fair housing law and airline deregulation. Today, he is an unusual kind of judge: one with a deep personal attachment to the legislative process. That makes him a particularly interesting figure in the current debate over how "activist" judges should be.

Justice Breyer has just published a book, "Active Liberty: Interpreting Our Democratic Constitution," which is in part a response to those, like Justice Antonin Scalia, who believe the Constitution should be interpreted based on the "original intent" of the founders. But "Active Liberty" stands on its own as a provocative and well-argued case for reading the Constitution in light of the founders' greatest concern: giving the people the power to govern themselves.

In this time of transition on the court, which is getting two new members, including a chief justice to succeed William Rehnquist, Justice Breyer's book could help chart a path in which the court starts to interpret the Constitution in ways that strengthen American democracy.

"Active liberty," according to Justice Breyer, is the ability of ordinary citizens to play a role in government decisions. As he sees it, the Constitution's drafters were most interested in creating a government that remained under the control of, as the first three words of the document say, "We the People."

Originalists like Justice Scalia see the Constitution as a set of rights and rules that were frozen in time when they were written. Justice Breyer argues that the better What-would-the-founders-do? approach is to interpret the Constitution in ways that promote its essential purpose: helping citizens get the knowledge and power they need to influence government policies on important issues.

Justice Breyer applies the theory to specific cases. The right to free speech, he argues, should be interpreted in ways that help people exchange the information they need to govern themselves. Political speech is central to this process, and should be highly protected, he says, while "commercial speech" like advertising can be more regulated. He argues that campaign finance laws could survive many First Amendment challenges because they promote integrity in politics, which is a good thing for active liberty.

Promoting active liberty does not mean allowing the majority to run roughshod over minorities. It calls for taking special care that all groups have a chance to fully participate in society and the political process. Discussing the recent University of Michigan affirmative action cases, Justice Breyer contrasts an opinion by Clarence Thomas, arguing that the Equal Protection Clause requires government actions to be "colorblind," with one by Ruth Bader Ginsburg, more in the active liberty spirit, that sees a role for race-based distinctions intended to help groups "long denied full citizenship."

There is a real need on the court for this kind of intellectual counterweight to Justice Scalia and his original intent theories. Justice Breyer is also providing a long-overdue response to politicians' bumper-sticker take on the courts: that conservative judges "interpret" the law, while liberal judges "make" it. (In reality, Justice Scalia has been one of the justices most willing to strike down Congressional statutes, while Justice Breyer has been the least willing.)

Justice Breyer may also find some unexpected allies on the court. Justice Anthony Kennedy, a moderate conservative, has shown some inclination to think in active liberty terms, particularly in his rulings on gay rights and the juvenile death penalty. And at his confirmation hearings, John Roberts talked about the importance of deferring to the political branches, saying that "a certain humility should characterize the judicial function."

In one of the book's most potent images, Justice Breyer argues that difficult public policy questions should be resolved through a great national conversation - what Alexis de Tocqueville described as the "tumult" that "you find yourself in the midst of" when "you descend ... on the soil of America." Through the Constitution, he says, the courts can help that conversation along. What we need more of, "Active Liberty" insists, is not activist judges, but activist citizens.