Maybe you’ve heard a friend of yours say something like the scenario presented in this quick video:

Click here to download a transcript for this video

As the video establishes, this is a case where logic is misapplied. Claiming that, because his cigarette-smoking grandfather lived a long life, studies don’t mean anything about the relationships between smoking and cancer, is a pretty clear violation of logic.  It presents an argument in what sounds like a logical way, but it’s very easy to disprove.

Watch for similar misapplications of logic in reading you do (or television you watch, or conversations you participate in).

These misapplications of logic—known as logical fallacies—occur frequently in reading and in daily life. Read through the list below to explore some of the most common ones.

• Hasty generalization: argues from limited examples or a special case to a general rule.
  • Argument: Every person I’ve met has ten fingers; therefore, all people have ten fingers.
  • Problem: Those who have been met are not representative of the entire population.
• Making the argument personal (ad hominem): attacking or discrediting the opposition’s character.
  • Argument: What do you know about the United States? You aren’t even a citizen.
  • Problem: personal argument against an opponent, instead of against the opponent’s argument.
• Red herring: intentionally or unintentionally misleading or distracting from the actual issue.
  • Argument: I think that we should make the academic requirements stricter for students. I recommend that you support this because we are in a budget crisis and we do not want our salaries affected.
  • Problem: Here the second sentence, though used to support the first, does not address the topic of the first sentence, and instead switches the focus to the quite different topic.
• Fallacy of false cause (non sequitur): incorrectly assumes one thing is the cause of another. Non Sequitur is Latin for “It does not follow.”
  • Argument: I hear the rain falling outside my window; therefore, the sun is not shining.
  • Problem: The conclusion is false because the sun can shine while it is raining.
• If it comes before it is the cause: believing that the order of events implies a causal relation.
  • Argument: It rained just before the car died. The rain caused the car to break down.
  • Problem: There may be no connection between the two events.
• Two events co-occurring is not causation (cum hoc ergo propter hoc): believing that two events happening at the same time implies a causal relation.
  • Argument: More cows die in the summer. More ice cream is consumed in summer months. Therefore, the consumption of ice cream in the summer is killing cows.
  • Problem: No premise suggests the ice cream consumption is causing the deaths. The deaths and consumption could be unrelated, or something else could be causing both, such as summer heat.
• Straw man: creates the illusion of having refuted a proposition by replacing it with a superficially similar proposition (the “straw man”), and refuting it, without ever actually refuting the original.
  • Argument: Person A: Sunny days are good. Person B: If all days were sunny, we’d never have rain, and without rain, we’d have famine and death. Therefore, you are wrong.
  • Problem: B has misrepresented A’s claim by falsely suggesting that A claimed that only sunny days are good, and then B refuted the misrepresented version of the claim, rather than refuting A’s original assertion.
• The false dilemma: the listener is forced to make a choice between two things which are not really related or relevant.
  • Argument: If you are not with us, you are against us.
  • Problem: The presentation of a false choice often reflects a deliberate attempt to eliminate any middle ground.