Why closed-mindedness is an imperative for the left.

By intentionally refusing to challenge, disprove, understand or even acknowledge the existence of the other side's argument, you allow that argument to grow in strength and win converts.

When pollsters ask Republicans and Democrats whether the president can do anything about high gas prices, the answers reflect the usual partisan divisions in the country. About two-thirds of Republicans say the president can do something about high gas prices, and about two-thirds of Democrats say he can't.

But six years ago, with a Republican president in the White House, the numbers were reversed: Three-fourths of Democrats said President Bush could do something about high gas prices, while the majority of Republicans said gas prices were clearly outside the president's control.

The flipped perceptions on gas prices isn't an aberration, said Dartmouth College political scientist Brendan Nyhan. On a range of issues, partisans seem partial to their political loyalties over the facts.

It’s one of the great assumptions underlying modern democracy that an informed citizenry is preferable to an uninformed one. If people are furnished with the facts, they will be clearer thinkers and better citizens. If they are ignorant, facts will enlighten them. If they are mistaken, facts will set them straight.

Maybe not. Recently, a few political scientists have begun to discover a human tendency deeply discouraging to anyone with faith in the power of information. It’s this: Facts don’t necessarily have the power to change our minds. In fact, quite the opposite. In a series of studies in 2005 and 2006, researchers at the University of Michigan found that when misinformed people, particularly political partisans, were exposed to corrected facts in news stories, they rarely changed their minds. In fact, they often became even more strongly set in their beliefs. Facts, they found, were not curing misinformation. Like an underpowered antibiotic, facts could actually make misinformation even stronger.

This bodes ill for a democracy, because most voters — the people making decisions about how the country runs — aren’t blank slates.