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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
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”
Culture and Logic
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?