But what about merely irrelevant statements, or only implicitly misleading ones? Standard economic models say such claims are, well, irrelevant, so there should be no need to regulate them. But according to recent behavioral research, it’s a distinction without a difference.

Although cigarette advertisements, for example, typically portray smokers as young, healthy and attractive, smoking can make people look older and less healthy. Such ads make no explicitly false claims, but that doesn’t make them less misleading, even for informed consumers.

More troubling are instances in which politicians employ patently false statements to shift the terms of important public debates. Decades before President George W. Bush tried to privatize Social Security, for example, Democratic presidential candidates regularly frightened Florida seniors with groundless accusations that their opponents would gut the program.

Of course, politicians of both parties have long taken liberties with the truth. But as even conservative political commentators have begun to point out, Republicans have lately been far more aggressive in stretching traditional boundaries. When Sarah Palin said that if health care reform legislation were adopted, her parents and her child with Down syndrome “will have to stand in front of Obama’s ‘death panel’ so his bureaucrats can decide, based on a subjective judgment of their ‘level of productivity in society,’ whether they are worthy of health care,” most people probably realized the president had made no such proposal. Her statement nonetheless shifted the terms of the debate, making it harder for legislators to focus on genuinely relevant issues.

CAN anything be done? For a variety of practical reasons, legal sanctions promise little protection against blatantly false statements. It is helpful, to be sure, when journalists call out politicians who stray too far from the truth. But merely knowing that a statement is false doesn’t nullify its impact. To be effective, a remedy must act prospectively. It must discourage people from making false statements in the first place.

Economists have long recognized that social sanctions are often an effective alternative to legal and regulatory remedies. As Adam Smith argued, moral sentiments are extremely powerful drivers of human behavior. People who know they’ll be ridiculed for telling untruths are more likely to show restraint.