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Do Your Own » Logical Fallacies

In drawing your connections between cause and effect, you will want to watch out for logical fallacies. Fallacies are errors in reasoning or in the use of evidence. Here are a few:

Hasty generalization is the fallacy of basing a conclusion on too little evidence. If your flight to Chicago on Supersky Airlines is delayed, that does not entitle you to claim that Supersky Airlines is always late. You need more than a single case to support such a conclusion.

Overgeneralization is the fallacy of assuming that all members of a group do what most members of the group do. Many Japanese eat raw fish regularly, but you overgeneralize if you claim that all Japanese eat raw fish. Similarly, not all Italians like spaghetti, and not all Republicans support George W. Bush. Be cautious in using such words as all, no, always, and never. Instead, qualify broad generalizations with words like many, most, and few, or frequently, often, rarely, and seldom.

Non sequitur (Latin for "it does not follow") is the fallacy of claiming a conclusion that does not follow logically from the premises. One example might be a statement like the following:"The chorus wore such ugly costumes that I was surprised they sang so well." What does clothing have to do with how well people sing? You must establish a clear connection between premise and conclusion before readers will accept such a cause and effect relationship.

Post hoc, ergo propter hoc (Latin for "after this, therefore, because of this") is the fallacy of claiming that one event is the cause of another from the mere fact that the first occurs earlier than the second. For example, "I found a four-leaf clover, so I got an A on my Spanish test."

Begging the question is the fallacy of offering a conclusion that simply rewords the premise. If you claim that parallel lines never meet because they are parallel, you are restating the premise instead of providing evidence for it.

False analogy is the fallacy of comparing two things that are not sufficiently alike to be fairly compared. If you claim that the United States is becoming as sexually permissive as ancient Rome and, therefore, will fall just as Rome did, you are offeringa false analogy. The comparison concentrates on a single similarity, but ignores all differences. A good analogy clarifies an unfamiliar or difficult concept by comparing it with something more familiar or more easily understood.

Either/or is the fallacy of offering only two choices when more possibilities exist. If you adopt the political slogan "America, love it or leave it," you are guilty of this fallacy. It is possible to love a country and leave it or live in a country without loving it. The either/or fallacy most often occurs when we attempt to reduce a complex issue to its bare essentials. To be sure, if there are only two possibilities -- for example, either you are pregnant or you are not -- there is no fallacy.

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