Reasoning
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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?. Deductive Reasoning. Reasoning from general to specific Drawing conclusions from stated premises.

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Reasoning

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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?


Deductive Reasoning

  • Reasoning from general to specific

  • Drawing conclusions from stated premises


Syllogism

  • logical argument with two premises and a conclusion

    • All Wongas are rice farmers.

    • Smith is a Wonga.

    • Is Smith a rice farmer?


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


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”


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


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


Atmosphere Effect

  • All A are B

  • All C are B

  • *Therefore, all A are C


Inductive Reasoning

  • Reasoning from specific observations to general conclusions

  • Scientific reasoning

  • Use of heuristics in everyday life


Heuristics

  • Shortcuts in reasoning based on knowledge

  • May result in errors

  • Fast


Availability Heuristic

  • Probability judgments are based on how easy it is to remember events (Tversky & Kahneman, 1973)

  • McKelvie’s (1997) famous name experiment


Representativeness Heuristic

  • Probability judgments are based on the similarity of an event to a population

  • The bank teller problem (Tversky & Kahneman, 1983)


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


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)


Learning Categories

  • Conservative focusing: change one feature at a time

  • Focus gambling: change multiple features at a time


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)


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


Tversky and Kahneman (1981)


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)


Examples of Irrational Reasoning

  • ad hominem

  • majority must be right

  • straw man


Evolutionary Psychology

  • How can biases in reasoning be adaptive?


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