Deviations from the truth vary. Someone might neglect to tell the whole truth by omitting important information, exaggerate to impress others, downplay the significance of something known to be crucial, say something in a deliberately ambiguous way to provide an out, or tell a barefaced lie.

You'll find all of this online.

In the 18th century the philosopher Immanuel Kant argued that all lying is unethical under all circumstances. Kant was a subtle thinker, but most people, I believe, recognize that the complexity of human relations and the realities of the free market, democracy, and international relations occasionally require deviations from the absolute truth to grease the wheels of a civil society and peaceful world.

Lying also has a biological aspect. Deception is common in many species as a way of attracting or fooling prey or mates or otherwise promoting your survival or that of your offspring. But deception that crosses the line, however that line is defined by any given society, is deemed unethical or illegal or both and has consequences.

It's also in our interest to be good at deception detection.

The Web can help with fact checking and truth testing. This can be especially useful during a presidential election year, when the temptation for very public figures to deviate from the truth can be overwhelming. FactCheck.org (www.factcheck.org), a project of the Annenberg Public Policy Center, was one of the first political fact-checking Web sites, founded in 2003. It describes itself as "a nonpartisan, nonprofit 'consumer advocate' for voters that aims to reduce the level of deception and confusion in U.S. politics."

Traditional gatekeepers of the news--daily newspapers--are also getting in on the action, perhaps as a way to differentiate themselves from strictly Internet-based sources of news. Many newspapers across the country are launching or joining fact-checking initiatives, which are typically open to the public as well.

Two of the most visible newspaper-based fact-checking operations are PolitiFact (www.politifact.com), launched by the Tampa Bay Times, and Truth Needle (www.seattletimes.nwsource.com/html/truthneedle), launched by the Seattle Times.

Misinformation comes in other forms besides the political. The best-known site for getting to the bottom of "urban legends, folklore, myths, rumors, and misinformation" is Snopes.com (www.snopes.com), founded by a husband and wife team of researchers and writers, Barbara and David Mikkelson. You can do a keyword search or browse through categories from autos to weddings.

Trying to dispel one of the wackier rumors about Snopes.com itself---that the site is funded by billionaire Marxists, the Mikkelsons point out that they receive revenue strictly though advertising and are completely independent.

One of the oldest pieces of advice to avoid getting duped by false information is to resist believing everything you read. This is especially true on the Internet, where anybody can play expert and where the pressure to break genuine news often leaves little time for fact checking even by reputable sources.

If the information is both surprising and important, you should check it against at least two other sources. If it involves a brand new development, it's generally best to avoid acting on it until the dust settles and the development's true nature becomes clearer.

There are plenty of good sites on the Web for getting background material for help in determining the accuracy of information you come across.

Wikipedia (www.en.wikipedia.org/wiki) is the world's largest and most popular encyclopedia, with content generated by users, from experts to hobbyists. Though it's often pooh-poohed by teachers and editors for its lack of academic rigor, Wikipedia has a self-correcting mechanism that eliminates much inaccuracy.

Cousins to encyclopedias, almanacs are great for checking facts and figures. The best online almanac is Infoplease (www.infoplease.com), a descendant of the paper almanac Information Please and before that a radio quiz show of the same name that first aired in 1937.

The advertising-supported Infoplease is owned by Pearson, which publishes the Financial Times and numerous books through the Penguin Group of book publishers. At Infoplease you can search by keyword through the entire site or browse through various categories. There's also a biographical dictionary, atlas, compact encyclopedia, and homework center for kids.

But if you're delving deeply into the background of people or words, specialized sites will typically take you further. Popular sites include Bio.com (www.biography.com), Dictionary.com (www.dictionary.reference.com), and Acronym Finder (www.acronymfinder.com).