Readings

Misuses of Logic

  1. Begging the question: to prejudge an issue by using loaded language or stating something that is self-evident.

E.g., “It is inadvisable to let hardened criminals out of prison prematurely so they can renew their war on society.”

  • “The policy of releasing prisoners on probation probably has not justified the social risks it involves.”
  1. Either/Or reasoning: to unfairly limit the options available.

E.g., “We must legalize abortion or the world will become disastrously overpopulated.”

  1. Post hoc, ergo propter hoc (After this, therefore becauase of this): to claim, with no evidence, that y followed x, therefore x caused y.

E.g., “I must be a good influence. The day I started work at ABC Investments, the company’s stocks rose.”

  1. Generalization: to make large claims based on insufficient data.

E.g., “The only two redheads I worked with were over 6 feet tall. All redheads must be tall.”

  1. False analogy: To assume that two circumstances or ideas are alike in all respects.

E.g., “She’ll make a great Secretary of Agriculture—she’s lived on a farm all her life!”

  1. Non sequitur: to mistake an interference for a logically sound conclusion.

E.g., “Serendipity State U. has a new library, pool and Science Center. Enrollments are definitely going to increase.”

  1. Self-contradictions: to include in an argument mutually exclusive premises.

E.g., “The government should control this unmanageable situation.”

  1. Confusion between fact and value judgment: to fail to distinguish between what can be observed, measured and tested—a fact—and our attitude to the fact—value judgment. Both are important, but they should not be confused.

E.g., “Your hair is long (fact). I don’t like your hair long (judgment).”

“Your hair is too long (≠ fact).”

  1. Ignoring the question, or rambling: to present details or facts that do not support the thesis.

E.g., “We should do more to help the poor help themselves. Of course, the Bible says we’ll always have the poor with us, even though it doesn’t say we should give them everything we have.”

  1. Ad hominem (“To the person”): to try to disprove an argument by attacking the person who presents it.

E.g., “John Doe is allegedly an adulterer and a liar; his arguments against sales tax are worthless.”

  1. Ad populum (“to the people”): to appeal to popular emotions, prejudices or beliefs.

E.g., “The American people are generous, compassionate and freedom-loving. To reflect the will of the people, immigration laws should be abolished.”

  1. Bandwagon: to argue that the “crowd must be right.”

E.g., “This novel has been #1 on the best-seller list for weeks. You must read it!”

  1. Appeal to prestige: to rely in an argument on testimony of famous people, rather than on facts.

E.g., “Tiger Woods eats this cereal, so it is better than others.”

  1. Ambiguity: to make a claim in which the meaning is unclear because more than one interpretation is possible.

E.g., “John McCain likes Bush better than his wife.”

  1. Equivocation: to use a word or expression in two different senses within the same argument.

E.g., “Americans believe that we have a right to pursue happiness, and we should do what is right. So, let’s make happiness our goal in life.” (“right” has two meanings)