1. Reasoning

2. 2 Types of Reasoning Deduction Induction
Deductive arguments: If the premises are true (and the argument's form is valid) then the conclusion must be true.
Induction
Inductive arguments: The premises support the conclusion, but do not guarantee that it is true.

3. Deduction
Syllogisms
Conditional Reasoning

4. Categorical Syllogisms
Major premise, minor premise, conclusion
Can be represented with Venn diagrams (all, some, none)
Aristotle: Prescriptions for reasoning correctly with syllogisms
Empirical observations: Descriptions of actual reasoning with syllogisms

5. Reasoning with Syllogisms
"Atmosphere effect"
"Some parents are scientists; All scientists are drivers, therefore:"
Some parents are drivers
Some drivers are parents
Both conclusions are valid, but the first is more likely to be drawn.
One explanation: Johnson-Laird & Steedman (1979) model of syllogistic reasoning; checking validity of arguments is done by checking for a "path" from premises to conclusion.

6. Reasoning with Syllogisms
High-imagery and high-relatedness syllogisms are solved more accurately than more abstract syllogisms (Cement & Falmagne, 1986)
High relatedness: Some politicians are lawyers.
Low relatedness: Some politicians are farmers.

7. Conditional Reasoning (If-Then) Prescription: Truth Tables
A (It rained today)
B (The sidewalk is wet)
If A then B (If it rained today then the sidewalk is wet)
True
False

8. Conditional Reasoning: Prescriptive Rules
Propositional Logic
Modus Ponens
If A, then B A
Therefore B
Modus Tollens
Not B
Therefore not A

9. Conditional Reasoning: the Wason Selection Task
Subject is shown 4 cards: E F
Each card has a letter on one side, a number on the other.
Hypothesis: "If a card has a vowel on one side, it has an even number on the other."
Task: Choose the cards you should turn over to test this hypothesis
Which cards would you turn over? Click here for the correct answer and a frequent error.

10. Hypothesis Testing and the Confirmation Bias (Wason, 1960)
“2, 4, 6” – What is the rule?
Generate lists of 3 numbers to test your rule.
Subjects hypothesised the rule "ascending by 2" and generated test lists that fit the rule to test it.
The actual rule was "any ascending sequence"; so 2, 4, 5 would fit the rule also, but subjects never tried this.
The tendency to construct tests consistent with our hypotheses is the confirmation bias.

11. Inductive Reasoning
Estimating probabilities -- because inductive reasoning involves having evidence that supports but does not prove a conclusion, correct inductive reasoning is a matter of correctly estimating the probability that the conclusion is true based on the available evidence.
Bayes' Theorum – a prescriptive rule

12. Deviations from Correct Bayesian Reasoning
Neglecting Base Rates
Under-estimating the importance of new evidence

13. Why do we make these mistakes?
Heuristics – mental shortcuts
Availability
Adjustment and Anchoring
Representativeness
Why do we use heuristics?