Is US a nation of liars? Casey Anthony isn't the only one.

In court cases, witnesses pledge to tell "the truth, the whole truth, and nothing but the truth." In Judeo-Christian tradition, there's the Ninth Commandment – "thou shalt not bear false witness." Most parents admonish their children to be honest.

But as the news fills with one example after another of people – both humble and mighty – telling lies, it's easy to wonder: Can America even see the truth anymore, let alone tell it?

Consider an array of recent examples:

•In the trial for Casey Anthony, who was charged with killing her 2-year-old daughter, the prosecution and defense agreed that Ms. Anthony had told numerous lies while her daughter was missing. In the end, the jury reached a verdict that cleared her of all charges – except those about giving false information to law enforcement officers.

•In Atlanta, investigators have named 178 teachers and principals who allegedly changed student test answers to collect bonuses and make their schools look good. More than half the teachers, the investigators' report said, lied about or attempted to cover up their malfeasance.

•The sexual assault allegations against Dominique Strauss-Kahn, the former International Monetary Fund chief, started falling apart after prosecutors concluded that the alleged victim, an immigrant from Guinea, lied about a past rape allegation and falsified immigration papers.

•In June, New York Rep. Anthony Weiner resigned from Congress after admitting that he hadn't been truthful about an embarrassing Twitter photo.

•Baseball slugger Barry Bonds was found guilty by a San Francisco jury in April of obstructing justice by giving an evasive answer to a grand jury looking into doping allegations. He may be retried on a more serious perjury charge.

•Roger Clemens, the seven-time Cy Young Award-winning pitcher, was also standing trial for statements he gave about doping – in his case, for allegedly lying to Congress by denying the use of steroids, despite a mountain of evidence against him. But on July 14, the judge in the case declared a mistrial. He set a Sept. 2 hearing to discuss where the case goes next, if anywhere.

Ethicists say there is, in some cases, moral justification for not quite living up to George Washington's "I cannot tell a lie" maxim. But the recent spate of lying scandals nevertheless hints at a deeper problem, some say: that serious lies and outright cheating have gotten so pervasive – or at least so well publicized – that they no longer register for many as a moral failing. Yet the justice system, the political system, and even democracy itself can't function if they're built on a foundation of fibs, insist legal experts, ethicists, and others.

"This culture of accepted cheating and lying tends to empower the people at the top and ... amplifies the inequality in our society, all of which has negative ramifications," says David Callahan, author of "The Cheating Culture." "It sort of moves us more toward Russia or Brazil with oligarchs who can do whatever they want. We're not that bad, but we could be headed in that direction."

Detailed statistics on lying are hard to come by, frankly because its very nature is to deceive and go unnoticed. But concerns have been rising for at least two decades about the moral fraying that leads Americans of all stripes to forgo the truth when faced with tough questions, especially from institutions like the courts or the media.

Still, one study seems to affirm that Americans, on the whole, try their best to tell the truth. A 2009 report in the Human Communication Research journal found that 5 percent of people told 50 percent of lies, causing the authors to conclude that "most reported lies are told by a few prolific liars."

Yet America's moral compass may be wavering, some say. The Josephson Institute of Ethics's biannual survey of teens has found one key paradox: While 92 percent of students believe their parents want them to do the right thing, more than 8 in 10 confessed they had lied to a parent about something significant.

Moreover, 76 percent of Americans say the country's moral values regarding cheating and lying are getting worse, according to a 2010 Gallup poll.

"Mounting evidence suggests that the broad public commitment to telling the truth under oath has been breaking down ... a trend that has been accelerating in recent years," writes novelist and journalist James Stewart in his new book, "Tangled Webs: How False Statements Are Undermining America." "Perjury," Mr. Stewart continues, "is committed all too often at the highest levels of business, media, politics, sports, culture – even the legal profession itself – by people celebrated for their achievements, followed avidly by the media, and held up as role models."

Those scandals "at the highest levels" are reflected all too often in the broader culture. A recent insurance industry study showed that 8 percent of registered farm vehicles, which get a 20 percent break on insurance premiums, are Porsche Carreras and other high-end cars parked in suburban garages.

Watching others get ahead by telling lies, ethicists argue, provides some people with moral justification for following suit.

"At a certain point, you're watching all these jerks and you say, 'What am I, a schmuck?' " says Douglas Porpora, a sociology professor at Drexel University in Philadelphia who studies moral and political communication. "A lot of people want to do the right thing, and after a while they say, 'You know what? I'm going to follow the jerks.' "

Adds Mr. Callahan: "There just don't seem to be a lot of moral downsides to cutting corners" to improve lifestyles. "Every day there's new evidence of successful people who have cheated to get ahead, and it creates cynicism."

One solution to a lying epidemic, Stewart contends, is for institutions like the courts to come down harder on liars. Among other things, this could mean ending "slaps on the wrist" for white-collar criminals who weave webs of lies in their quest for fame and riches.

"The public is looking at the Clemens and Bonds cases and saying, 'Who cares about steroids anymore?' " says Peter Keane, a law professor at Golden Gate University in San Francisco. "But then you look at what the government is concerned with, like in the Bonds case, where someone comes in and takes an oath before a grand jury and [then conducts himself as Mr. Bonds did]. If they get a pass on that, that goes to the heart and integrity and operation of the justice system in the United States."

Yet in a country that prizes free speech, the truth is that lies are difficult to prosecute. Last year, the Ninth Circuit Court of Appeals ruled unconstitutional parts of the 2005 Stolen Valor Act, signed by President Bush to stop people from lying about military commendations.

"The government cannot criminalize a statement simply because it is false, no matter how important the statement is," Chris Beall, an attorney for the American Civil Liberties Union, wrote in a friend-of-the-court brief.

Despite what some see as cultural ambivalence about lying, Americans may at least be thinking a bit harder before twisting the truth. The latest Josephson report, for example, "shows some improvement in ethical behavior," according to the authors.

One possibility is that the constant parade of truth-twisting scandals may be causing Americans to think harder about personal morals. "I think there is a sense of cultural disappointment in these breaches and the lying that comes after them," says Professor Porpora.