How To Spot a Logical Fallacy Part 2

Argument from fallacy (also known as the fallacy fallacy) – the assumption that, if an argument is fallacious, then the conclusion is false.

  • If P, then Q.
  • P is a fallacious argument.
  • Therefore, Q is false
  • This is a special case – A fallacious argument can still have a consequent that happens to be true. The fallacy is in concluding the consequent of a fallacious argument has to be false.
    • All cats are animals. Ginger is an animal. Therefore, Ginger is a cat.
    • You are incorrect. Therefore, Ginger is not a cat.
  • Exception: At times, fallacies are used by those who can’t find a better way to support the truth claims of their argument — it could be a sign of desperation.  This can be evidence for them not being able to defend their claim, but not against the claim itself.

Conjunction fallacy – the assumption that an outcome simultaneously satisfying multiple conditions is more probable than an outcome satisfying a single one of them.

  • Linda is 31 years old, single, outspoken, and very bright. She majored in philosophy. As a student, she was deeply concerned with issues of discrimination and social justice, and also participated in anti-nuclear demonstrations.
    • Which is more probable?
  1. Linda is a bank teller.
  2. Linda is a bank teller and is active in the feminist movement.
  • The majority of those asked chose option 2. However, the probability of two events occurring together (in “conjunction“) is always less than or equal to the probability of either one occurring alone

Masked-man fallacy – if one object has a certain property, while another object does not have the same property, the two objects cannot be identical

  • Premise 1: Lois Lane thinks Superman can fly.
  • Premise 2: Lois Lane thinks Clark Kent cannot fly.
  • Conclusion: Therefore Superman and Clark Kent are not the same person.

Imagine Superman, who is also Clark Kent, flew to Italy for a slice of pizza.  If we said, “Clark Kent flew to Italy for pizza” we would be right, because of the extensional context of that statement.  Conversely, if we said, “Lois Lane thinks Superman flew to Italy for pizza”, we would still be making a true claim, although the context is now intensional as indicated by the term, “thinks”.  Now if we said, “Lois Lane thinks Clark Kent flew to Italy for pizza”, we would be wrong and would have committed this fallacy because Lois does not believe that, even though extensionally it is the case (this is after the kiss that wiped her memory of Clark being Superman).

  • Exception: Technically, none
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