Why do we lie? Let Alex Kozinski, the chief judge of the U.S. Court of Appeals for the 9th Circuit in San Francisco, count the ways.

“We lie to protect our privacy (‘No, I don’t live around here’); to avoid hurt feelings (‘Friday is my study night’); to make others feel better (‘Gee, you’ve gotten skinny’); to avoid recriminations (‘I only lost $10 at poker’),” Kozinski wrote recently in a case about an inveterate liar named Xavier Alvarez who, just to drive home the point, is also known as Javier Alvarez.

Kozinski listed 28 other reasons we avoid the truth, including to “avoid a nudnick” and to “defeat an objective (‘I’m allergic to latex’),” and ending sweetly with “to maintain innocence (‘There are eight tiny reindeer on the rooftop’).”

Kozinski’s entertaining treatise was in service to his point about the Constitution.

“If all untruthful speech is unprotected . . . we could all be made into criminals, depending on which lies those making the laws find offensive,” he wrote. “And we would have to censor our speech to avoid the risk of prosecution for saying something that turns out to be false.

“The First Amendment does not tolerate giving the government such power.”

Kozinski’s is the first appeals court to examine a law that seems likely to be on the way to the Supreme Court: the Stolen Valor Act, passed by Congress in 2005 to deal with an apparent proliferation of people falsely claiming to be military heroes.

The act allows a fine and/or a six-month prison term for someone who “falsely represents himself or herself, verbally or in writing, to have been awarded any decoration or medal authorized by Congress for the Armed Forces of the United States.”

The penalty increases to a year in prison if the person lies about a Purple Heart, a Medal of Honor or another particularly high honor.

There’s no question Alvarez lied. After winning a seat on Southern California’s Three Valleys Municipal Water District board of directors in 2007, he introduced himself by saying: “I’m a retired Marine of 25 years. I retired in the year 2001. Back in 1987, I was awarded the Congressional Medal of Honor. I got wounded many times by the same guy.”

None of that was true. But a district judge overturned Alvarez’s conviction by declaring the law a violation of the First Amendment. A panel of the 9th Circuit agreed, and earlier this month the full court refused to reconsider the panel’s decision.

Judge Diarmuid O’Scannlain and six other 9th Circuit judges said their colleagues were wrong. He said the decision to find the law unconstitutional “runs counter to nearly forty years of Supreme Court precedent” in which the court “has steadfastly instructed that false statements of fact are not protected by the First Amendment.”

Both sides cite the court’s landmark free-speech cases. Judge Milan D. Smith Jr., who agreed the law was unconstitutional, said 1964’s New York Times Co. v. Sullivan made clear that “false speech is not subject to a blanket exemption from constitutional protection.”

He said the court has never included “false statements of fact” to be among the classes of speech unprotected by the First Amendment. He noted that as recently as last year’s decision in United States v. Stevens, the court’s list of “well-defined” unprotected speech included only “obscenity, defamation, fraud, incitement and speech integral to criminal conduct.”

O’Scannlain and the dissenters point to cases decided after Sullivan, including Gertz v. Robert Welch, Inc ., in which the court said that “there is no constitutional value in false statements of fact.”

Judge Ronald M. Gould said he believed the Stolen Valor Act could be sustained because “the power of Congress is necessarily strong” in a military context and there is a “lack of any societal utility in tolerating false statements of military valor such as those made by Alvarez.”

Gould acknowledged that each side can make a case from the words of Supreme Court precedents and said it “remains open for the court” to clarify its First Amendment doctrine.

That seems likely. The U.S. Court of Appeals for the 4th Circuit is scheduled in May to hear an appeal from a decision by a Virginia district judge that the law passes constitutional tests. A federal judge in Denver found just the opposite.

Until then, the task of punishing the liars might be up to such phony-hunters as Doug Sterner of Alexandria, profiled by The Washington Post last year, and Web sites such as ReportStolenValor.org. There appears to be no shortage of leads.