U.S. Supreme Court Justice Stephen G. Breyer paid a hushed visit to Harvard Law School yesterday, calling Bush v. Gore the “most stressful” case during his 12-year tenure and delivering a short address on the high court’s operations.

Breyer’s speech to Climenko Professor of Law Charles J. Ogletree’s criminal law class was kept secret from everyone, including Ogletree’s students, until minutes before it began. After a warm greeting from the first-year students, Breyer, a Law School graduate, delivered a relaxed talk about life as a Supreme Court justice.

When asked to choose the most important case of his tenure, Breyer pointed to Bush v. Gore, the 2000 case that ended the Florida recount, because the court had to effectively decide a presidential election in a short time span.

But in terms of social impact, Breyer chose the 2003 University of Michigan affirmative action cases, specifically the ruling upholding Michigan Law School’s admissions policy.

“The way the court works is very future related,” Breyer explained.

Breyer devoted most of his speech to outlining the court’s review process, from the time an attorney files an appeal to when a decision is reached and a written opinion is issued.

Deciding which cases to review is “more mechanical than people think,” Breyer said.

“If you were to go through my stack tomorrow, you’d be surprised at how much agreement there would be in the cases you would pick for the court to hear and the cases I would pick,” Breyer said. He added that because of the specificity of the criteria used by the court, choosing which cases to review is fairly straightforward.

The main criterion used by the court is whether a case would give “the country a uniform interpretation of federal law,” Breyer said. “We are not an error-correcting court.”

Breyer also shed light into the justices’ secret Friday conferences—where the nine meet to choose cases and deliberate opinions—and how the law clerks contribute to the court’s operations.

He said that all the appeals petitions that the court receives are read by one of the justices’ clerks. The clerks then write up a memo summarizing each case, which in turn is read by the justices. If four justices wish to hear a case, an hour of oral arguments is scheduled.

“The purpose for that hour is for us to ask questions,” Breyer explained.

Breyer also spoke about recent court decisions paring back the federal sentencing guidelines—decisions that Breyer has supported even though he is widely regarded as the architect of these rules. The court altered them because many lower court judges were not departing from the guidelines when the facts of their cases were atypical, he said.

“Making them advisory were really what they were supposed to be to begin with,” Breyer said. “It was a practical solution to the problem.”

Breyer, who still maintains a residence in Cambridge, is a former Law School professor.

—Staff writer Javier C. Hernandez contributed to the reporting of this article.

—Staff writer Paras D. Bhayani can be reached at pbhayani@fas.harvard.edu.