Reasoning

1. Reasoning • What is the difference between deductive and inductive reasoning? • What are heuristics, and how do we use them? • How do we reason about categories? • How do we make decisions?

2. Deductive Reasoning • Reasoning from general to specific • Drawing conclusions from stated premises

3. Syllogism • logical argument with two premises and a conclusion • All Wongas are rice farmers. • Smith is a Wonga. • Is Smith a rice farmer?

4. Logic of Syllogisms • If both premises are true, then a conclusion that logically follows from the premises is true • If the conclusion follows logically for every possible case, it is valid • Validity depends on the logical form, not on the content

5. Culture and Logic • People from cultures that emphasize experience answer: “I don’t know Smith, so I can’t say.” (Cole & Scribner, 1974) • People from cultures that emphasize logical structure answer: “Yes”

6. Belief Bias • Conclusions are more likely to be judged as valid if they are consistent with the person’s beliefs (Janis & Frick, 1943) • All poisons are bitter • Arsenic is not bitter • Therefore, arsenic is not a poison

7. Atmosphere Effect • The use of particular words in the premises can set a mood that influences what conclusion is drawn (Chapman & Chapman, 1959) • “All” premises suggest an “All conclusion” • “Some” premises suggest a “Some” conclusion

8. Atmosphere Effect • All A are B • All C are B • *Therefore, all A are C

9. Inductive Reasoning • Reasoning from specific observations to general conclusions • Scientific reasoning • Use of heuristics in everyday life

10. Heuristics • Shortcuts in reasoning based on knowledge • May result in errors • Fast

11. Availability Heuristic • Probability judgments are based on how easy it is to remember events (Tversky & Kahneman, 1973) • McKelvie’s (1997) famous name experiment

12. Representativeness Heuristic • Probability judgments are based on the similarity of an event to a population • The bank teller problem (Tversky & Kahneman, 1983)

13. The Bank Teller Problem • Linda is 31 years old, majored in philosophy, and is outspoken about political issues. Which is more likely? Linda is • A. a bank teller • B. a feminist bank teller

15. Confirmation Bias • Tendency to look for only for evidence that supports your belief • Most participants guessing the rule for a number series did not try sequences that would disconfirm their hypotheses (Wason, 1960)

18. Learning Categories • Conservative focusing: change one feature at a time • Focus gambling: change multiple features at a time

19. Categorization • Similarity Coverage Model (Osherson et al., 1990): knowledge of categories influences reasoning • More typical examples are more influential • More diverse examples are more influential • Specific knowledge can override these effects (Lopez et al., 1997)

20. Decision-Making • Framing Effects (Tversky & Kahneman, 1981) • Risk aversion strategy for choices framed in terms of gains • Risk taking strategy for choices framed in terms of losses

21. Tversky and Kahneman (1981)

22. Decision-Making • Focusing Illusion (Wilson et al., 2000) • One aspect of a situation is emphasized and other aspects are ignored • Life satisfaction ratings for others tend to focus on only the most obvious qualities (Schkade & Kahneman, 1998)

23. Examples of Irrational Reasoning • ad hominem • majority must be right • straw man

24. Evolutionary Psychology • How can biases in reasoning be adaptive?