Logical Fallacies

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A well-constructed argument avoids logical fallacies, flaws in the reasoning that will render the argument invalid. Following are some of the most common logical fallacies.

11 Logical Fallacies Explained

  1. Oversimplification. The tendency to provide simple solutions to complex problems. “The reason we have low unemployment today is the threat of war in Central America and the Middle East.”
  2. Hasty generalization is a generalization that is based on too little evidence or on evidence that is not representative. “It was the best movie I saw this year, and so it should get an Academy Award.”
  3. Post hoc, ergo propter hoc (“After this, therefore because of this”). Confusing chance or coincidence with causation. Because one event comes after another one, it does not necessarily mean that the first event caused the second. “Ever since I went to the hockey game, I’ve had a cold.” The assumption here is that going to the hockey game had something to do with the speaker’s cold when, in fact, there might be one or more different causes for the cold.  “Students who sit at the back of the class get lower marks to those who sit near the front of the class, so sit near the front!”  The fallacy here is the suggestion that simply sitting at the front of the class will improve a student’s grades.  Other factors seem more accountable: students who are likely to sit near the front of the class take a more active interest in the lessons, do their homework or make a more favorable impression on their teachers.
  4. Circular argument. Offering a restatement of an argument as a reason for accepting it. “Smoking is injurious because it harms the human body.” Or “There is only one argument that can be made to someone who rejects the authority of the Bible, that the Bible is true.” Paraphrase is not evidence!
  5. False analogy. Making a misleading analogy between logically unconnected ideas. “Of course he’ll make a fine coach. He was an all-star basketball player.”
  6. Non sequitur (“It does not follow”). An inference or conclusion that does not follow from established premises or evidence. “She is a sincere speaker; she must know what she is talking about.”
  7. Begging the question. You beg the question by assuming something that is actually your responsibility to prove, by building your argument on an undemonstrated claim. “Conservation is the only means of solving the energy problem over the long haul; therefore, we should seek out methods to conserve energy.” Or with a question: “Have you stopped beating your wife?”  Another form of begging the question is to make a claim and then insist that someone disprove it.  “How do you know that UFOs haven’t been visiting the earth since the time of the pyramids?”  In all argument, the burden of proof is on the person making the assertion.  It is a waste of your time to try to disprove a conclusion that was never proven to begin with.
  8. Argumentum ad Hominem is attacking the person and not the question at issue. “You are opposed to a war on terrorism because you are a coward!”  The speaker ignores the issue by attacking the man.  To avoid confusion, it should be added that an argument criticising a particular individual—a government official, a candidate, etc.—is probably not argumentum ad hominem; in such cases, the man is the issue.
  9. Extension is another way of ignoring the question. By extending the question, you can find yourself arguing a different subject altogether.  “If you outlaw guns, you might as well outlaw cars, too. And where would we be without cars?”  Are you arguing about guns or cars?  “I know Jean Chretien has his faults, but nobody is perfect!”  Are we discussing specific faults or attainment of perfection?  To arguments that ignore the question, the reasonable response is “Let’s get back to the issue.”
  10. Either/or thinking. The tendency to see an issue as having only two sides. “Used car salesmen are either honest or crooked.” When the debate begins on giving up civil liberties for the sake of increased security, we will probably hear: “Are you are in favor of getting rid of terrorism, or not?  Which side are you on, anyway?”  This is a clear oversimplification of the issue.
  11. Argumentum ad Populum is when writers appeal to popular sentiment or prejudices or claim that since everybody thinks a certain way, that way must be true. “Everyone knows that the private sector is more efficient than the public sector is!”  Just because everybody believes something, doesn’t make it true.  Everybody once thought the world was flat.  It turns out everybody was wrong.

Identify the Logical Fallacies

Here are 11 sentences containing logical fallacies. Try to identify which logical fallacy is contained in each.

  1. Everybody knows that men are smarter than women are.
  2. He must be telling the truth.  After all, he is very friendly.
  3. I am certain my teacher is a drug addict because I saw him take a pill once.
  4. I know cigarettes are bad for your health, but lots of things are bad for your health.  Take alcohol, for instance…
  5. If you didn’t cheat on your exam, then prove that you didn’t!
  6. It’s simple.  Metallica is the best because it is the best!  You can’t deny that.
  7. My brother says that marijuana should be legalized, but I disagree because he is an idiot.
  8. My sister broke a mirror last year.  That is why she has been very unlucky this year.
  9. She was an excellent student at university, so I’m sure she is a great teacher.
  10. The reason people get cancer is that they don’t eat enough carrots.
  11. If you don’t support sovereignty, it means you hate Quebec.