WASHINGTON  The anniversary will probably be observed in silence.

A week from Tuesday, when the Supreme Court returns from its midwinter break and hears arguments in two criminal cases, it will have been five years since Justice Clarence Thomas has spoken during a court argument.

If he is true to form, Justice Thomas will spend the arguments as he always does: leaning back in his chair, staring at the ceiling, rubbing his eyes, whispering to Justice Stephen G. Breyer, consulting papers and looking a little irritated and a little bored. He will ask no questions.

In the past 40 years, no other justice has gone an entire term, much less five, without speaking at least once during arguments, according to Timothy R. Johnson, a professor of political science at the University of Minnesota. Justice Thomas’s epic silence on the bench is just one part of his enigmatic and contradictory persona. He is guarded in public but gregarious in private. He avoids elite universities but speaks frequently to students at regional and religious schools. In those settings, he rarely dwells on legal topics but is happy to discuss a favorite movie, like “Saving Private Ryan.”

He talks freely about the burdens of the job.

“I tend to be morose sometimes,” he told the winners of a high school essay contest in 2009. “There are some cases that will drive you to your knees.”