Assumed Cause This faulty logic assumes that because one thing came before the other, the first must have caused the second.
Examples: "The lightning struck at 10:02, and the power disruption occurred at 10:03, so the lightning must have caused the power disruption" (Critical).
"Bennett was Secretary of Education when large drops in national achievement scores were recorded, so Bennett's policies must have been responsible for students across the country doing worse" (Critical).
Attacking the Messenger This faulty logic attacks the messenger in order to ignore the message. Our decisions should be based on a rational evaluation of the arguments with which we are presented, not on an emotional reaction to the person or persons making that argument. (Critical)
Examples: People that want this program are bleeding-heart liberals. People who don't believe in evolution are religious nuts. Those that criticize our military lack patriotism.
Circular Reasoning This is not logical at all. "It is because it is."
1 Step Examples: "I like vanilla ice cream best because it's my favorite kind" (Critical).
"Ralph Nader was the best candidate for president, because he was totally better than any of the others" (Critical).
2 Step Example: We know that these rocks are the oldest because they contain the oldest fossils. We know that these fossils are older than the other kinds because they were found in such old rocks.
Either/Or Fallacy This faulty logic assumes that there are only two choices. This is sometimes called the false dilemma.
Examples: "There are only two kinds of people in this world…"
People that don't support Affirmative Action are racists.
Either all religious expression must be removed from the public, or religion will be endorsed by the government.
This faulty logic assumes that if two things are alike in one or two ways, they must be alike in other ways.
Examples: Alcohol was banned in the thirties. Marijuana is banned now. We can expect all the same problems and we used to have, and we can solve this problem using the same methods.
"This man is against immigrants, just as Hitler was."
The conclusion the reader is supposed to draw is obvious. DO NOT compare ANYONE to Hitler. It's old.
Generalizations Don't try to draw a big conclusion from a small fact. One or two examples is not enough to form a generalization.
Examples: "Jana has been to San Diego several times, and the sky was always blue and the temperature ideal. The weather must be perfect in San Diego all the time" (Critical).
"Tina bought a used camera while she was up in Portland, and got a great deal. Portland must be a good place to buy used cameras" (Critical).
"The profit margin on HP's printer line has been a steady 25% for two years. We can assume, then, that the profits company-wide have also been 25%" (Critical).
"The poll from Orange County shows the governor winning in a landslide. I guess he will also win across the state just as easily" (Critical) .
Straw Man "The Straw Man fallacy is committed when a person simply ignores a person's actual position and substitutes a distorted, exaggerated or misrepresented version of that position" (Nizkor).
Examples: "My opponent never met a tax he didn't like."
Mr. Smith: "Poverty is one of the chief root causes of crime." Mr. Jones: "Smith believes that all poor people are criminals." (Wikipedia)
Jill: "We should clean out the closets. They are getting a bit messy." Bill: "Why, we just went through those closets last year. Do we have to clean them out everyday?" Jill: "I never said anything about cleaning them out every day. You just want too keep all your junk forever." (Nizkor)
Because the Problem Exists Don't tell the readers that must accept your solution to a problem merely because the problem exists.
Examples: "Two million people are unemployed. The government must increase welfare payments."