he sought to make the public case against the conservative doctrine of "originalism." He wrote two books arguing for a different interpretation of the Constitution and often debated conservative Justice Antonin Scalia in public. Scalia's often-repeated view was that the Constitution, as he put it, "is not living but dead," and it must be interpreted as the Founding Fathers would have. Breyer's view was that the founders understood perfectly well that nothing is static, citing for example, the Constitution's ban on cruel and unusual punishment.

"Flogging might have been fine in the 18th century," Breyer said in a 2010 interview with NPR. "That doesn't mean that it would be OK and not cruel and unusual punishment today."

What's more, he observed, even historians don't agree on what the founders meant at the time they wrote the Constitution.

"History is very often in these matters a blank slate or a confused slate, and if you want to govern the country by means of that history, then you better select nine historians and not nine judges to be on the court," Breyer told NPR. "And I'll tell you, those nine historians will very often disagree with each other."

The job of a Supreme Court justice, Breyer said, is to apply the Constitution's values to modern circumstances, using the tools of judging — precedent, text and the purpose of the constitutional provision at issue.

You can think of the Constitution as laying down certain frontiers or borders, he said. "And we're the border patrol."

"Life on the border is sometimes tough, and whether a particular matter — abortion or gerrymandering or school prayer — whether that's inside the boundary and permitted or outside the boundary and forbidden, is often a very, very difficult and close question," he said.