David French of National Review Online highlights a throwaway comment during recent U.S. Supreme Court proceedings that highlights an important legal principle.

Early in the oral argument, Justice Sotomayor went outside the evidence submitted to the court to ask NIFLA’s attorney, Mike Farris, questions about a website of a pro-life pregnancy center. Apparently, she’d been cruising the web on her own.

Moments later, Justice Kennedy responded, telling Justice Sotomayor, “Well, in this case I didn’t go beyond the record to look on the Internet because I don’t think we should do that, but I do have a hypothetical.”

Kennedy’s gentle rebuke hardly counts as a “conflict” in our polarized age, but it was important nonetheless. Court cases are fought over evidence and arguments submitted well in advance of court hearings. The reasons for this are obvious — by granting both sides the ability to examine the evidence and test the arguments, it minimizes the chance that cases are decided on the basis of unverified claims or misleading information. Simply put, judges should not act as free-lance investigators in the cases before them. In fact, this is judging 101.

Justice Sotomayor has adopted a level of aggression and a tone that’s sometimes different from her colleagues. It’s not unusual for justices to demonstrate open hostility to arguments they dislike, but Sotomayor’s level of contempt often goes beyond the norm.