1. Logic: Mental Models

2. How is logical reasoning done? Create concrete situations –Mental Models –Johnson-Laird and colleagues Build models of situations Find a description that characterizes the models –That description is the conclusion The more models that must be built, the harder the problem.

3. Some examples All Academics are Bean-counters All Bean-counters are Clean All Archers are Butchers Some Butchers are Camel Riders All Aardvarks are Boring No Candles are Boring

4. Illusions from the Paper Only one of the following premises is true about a hand of cards: There is a king in the hand or there is an ace, or both There is a queen in the hand or there is an ace, or both There is a jack in the hand or there is a 10, or both Is it possible there is an ace in the hand?

5. Problem 2 Suppose you know the following about a particular hand of cards If there is a jack in the hand, then there is a king in the hand, or else if there isn’t a jack then there is a king in the hand. There is a jack in the hand. What if anything follows?

6. Natural Language and Logic The previous problem arises because language does not work like logic –We do not evaluate what people say based only on the rules of logic. –We want to understand what people are trying to communicate with us.

7. Questions? How does this approach explain content effects? How does this approach explain truth effects? Does this tell us anything about reasoning that isn’t in logic situations?

8. Limitations of deduction Deductive reasoning is truth-preserving We are never 100% certain of the truth of any fact –Beliefs are based on observation and forms of reasoning that are not truth-preserving –If we are never 100% certain of truth, then there are limits on the value of truth-preserving operations.