Reasoning What is the difference between deductive and inductive reasoning? What are heuristics, and...

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?