Common Errors in Reasoning: A Guide to Logical Fallacies

Understanding Logical Fallacies

Logical fallacies are common errors in reasoning that undermine the logic of an argument. They can be illegitimate arguments or irrelevant points.

Common Logical Fallacies:

• Slippery Slope: A course of action that seems to lead from one action or result to another with unintended consequences. Example: If we allow the children to choose the movie this time, they are going to expect to be able to choose the school they go to or the doctors they visit.
• Hasty Generalization: A conclusion based on insufficient or biased evidence. Example: Kevin's grandparents do not know how to use a computer. Kevin thinks that all older people must be computer illiterate.
• Post Hoc Ergo Propter Hoc: A fallacy in which one event is said to be the cause of a later event simply because it occurred earlier. Example: Our soccer team was losing until I bought new shoes. We have not lost a game since I got my lucky shoes!
• Ad Populum: An emotional appeal that speaks to positive (religion, etc.) or negative (terrorism) concepts rather than real issues at hand. Example: Everybody on Earth believes that the Earth goes around the Sun, not the contrary. You would simply be wrong to believe otherwise.
• Red Herring: A diversionary tactic that avoids the key issues, often by avoiding opposing arguments rather than addressing them. Example: When you are late getting home past curfew, you distract your parents by talking to them about the weather – how cold it is, or how rainy it is.
• Straw Man: This move oversimplifies an opponent's viewpoint and then attacks that hollow argument. Example: Caroline says that she thinks her friends should not be so rude to the new girl. Jenna says that she cannot believe that Caroline is choosing to be better friends with the new girl than the girls who have always known her.
• Moral Equivalence: This fallacy compares minor misdeeds with major atrocities. Example: Somebody who participates in assisted suicide is as bad as Hitler.
• Genetic Fallacy: This conclusion is based on an argument that the origins of a person, idea, or theory determine its character, nature, or worth. Example: My sixth-grade teacher, Mr. Harris, said that all women are bad drivers, so it must be true.
• Begging the Claim: The conclusion that the writer should prove is validated within the claim. Example: Smoking cigarettes can kill you because cigarettes are deadly.
• Circular Argument: This restates the argument rather than actually proving it. Example: The Bible is true, so you should not doubt the Word of God.
• Either/Or: This is a conclusion that oversimplifies the argument by reducing it to only two sides or choices. Example: Drink water every day and be healthy, or continue to drink sodas and be unhealthy. Those are the only options.
• Ad Hominem: This is an attack on the character of a person rather than his or her opinions or arguments. Example: A parent who says that the teacher doesn't know how to teach because she graduated from a community college.