Informal Fallacies Lecture - Set 3 of 3

Introduction

• Last set of informal fallacies
• Next section: Propositional Logic (remaining semester topic)

Complex Question

• Answer to one question buried inside another
• Unasked question needs to be answered first
• Example: Does the referee know you just cheated?
  • Forces a yes to the unasked question (Did you cheat?)

False Dichotomy

• Presents only two choices when more options exist
• Example: Either you’re with us or you’re with the terrorists
  • Ignores possibility of other choices

Equivocation

• Conclusion relies on a word with two different senses
• Often used in puns
• Examples:
  • Good steaks are rare these days so don’t order yours well done
    • Mixes up rare (undercooked) with rare (hard to find)
  • Various jokes illustrating equivocation:
    • Chewbacca pun: rookie vs wookie
    • Conditioner pun: sham pooed
    • Cat pun: cheetah vs cheater
    • Spine pun: I got your back
    • Science pun: OMG (Oxygen and Magnesium)

Amphiboly

• Poorly constructed statement leading to problematic interpretation
• Example: George was interviewing for a job drilling oil wells in the supervisor’s office
  • Confuses drilling oil wells in an office vs. a job to drill oil wells elsewhere

Composition

• Assumes that properties of parts apply to the whole
• Example: Every sentence in this paragraph is well-written, so the paragraph is well-written
  • Well-written sentences may not form a well-written paragraph

Division

• Opposite of composition
• Assumes that properties of the whole apply to its parts
• Example: The students at Bradford College come from every state, therefore Michelle (a student) comes from every state
  • Incorrectly applies the whole’s property to a single part

Conclusion

• Recap of informal fallacies covered: complex question, false dichotomy, equivocation, amphiboly, composition, and division
• Assignment of homework
• Next topic: Propositional Logic