Reasoning: Basic concepts Flashcards
What is Deductive reasoning?
A judgement that something must be true if other statements are true.
e.g. All humans are mortal. Bill is a human. Therefore Bill is mortal
What is Inductive reasoning?
A judgement that some rule is probably true on the basis of experience.
E.g. Plato, Aristotle, Skinner were all mortal. They were all human. Therefore all humans must be mortal.
What is a Syllogism?
A basic reasoning puzzle - a set of statements (premises), and a conclusion.
- Does it follow?
E.g. Georges Cuvier: Parisian comparative anatomist - Student dressed as Devil claiming to devour him
1. All animals with hooves and horns are herbivores You have hooves and horns Therefore, you are a herbivore 2. No herbivore eats flesh You are a herbivore Therefore you don't eat flesh 3. All humans are flesh Cuvier is a human Therefore Cuvier is flesh 4. You don't eat flesh Cuvier is flesh Therefore you can't eat Cuvier
Is reasoning just logic, according to Logicism views?
No. Human reasoning =/= logic application
Logicism: “Logic is basis of human thought”
Adv: Always yields valid conclusions if premises are true (deductive reasoning)
- In logic, it doesn’t matter what A, B or C are in syllogisms: only context of premises matter
Disadv: always applies, so hard to account for errors.
Most people oppose this approach
What is the relationship between “true” and “valid”?
True is NOT equiv to Valid.
Valid concl = one that logically follows from premises
True concl = statement about the world.
Do not always match!
Sound concl = One with valid concl and true premises
In logic, only validity matters, but human reasoning is more than that.
How does plausibility affect our reasoning judgements?
“Logical” inferences are influenced by what we see as plausible.
e.g. If spot is a lizard then Spot is an animal. Spot is NOT a lizard. Therefore, Spot is NOT an animal
is logically equivalent (and invalid) with
If you clean up your room, I will give you $10. You do NOT clean up your room. Therefore, I do NOT give you $10.
How does negation affect our reasoning?
Negation make it harder for us to make reasoned judgements.
e.g. A) If it is Friday night, then Bill is drunk. It is Friday night. Therefore Bill is drunk.
B) If it is Friday night then Bill is drunk. Bill is not drunk. Therefore it is not Friday night.
Almost all endorse A), but many did not endorse B).
How do quantifiers affect our reasoning?
Quantifiers make it harder for us to reach logical conclusion.
E.g. A) NO CEOs are lazy. SOME rich people are lazy. Therefore, SOME CEOs are NOT rich people.
B) NO addictive things are cheap. SOME wines are cheap. Therefore, SOME addictive things are NOT wines.
10% of people accepted A), but 71% accepted B).
Quantifiers are harder, and what we believe to be true influences decision.
Why do we study syllogisms to study reasoning?
- Syllogisms reveal what we get right/wrong in reasoning
- Not all syllogisms are equal (e.g. negation and quantifiers)
- Reasoning like breathing for the mind: We constantly draw conclusions from premises, but are not aware
- We don’t just apply logic
What is the Wason selection task, and what does it reveal about the effects of context on reasoning?
Context matters!
Classic Wason selection task:
Rule: If a card has a vowel on one side then it has an even number on the other side. Which card(s) must be tested to see if the rule is true?
A B 4 7
- Only turn A: 33% (Affirming the sufficient)
- Turn “A” and “4”: 45% (Affirming the consequent)
- Turn “A” and “7”: 4% (Denying the consequent)
Correct answer: “A” and “7”
Systematic error in choice of cards to turn over.
Why do we always get the Wason selection task wrong?
Focus on vowels (A) and even numbers (4) because they are mentioned
Evans (1982): People do better when rule is stated as “If a card has a vowel on one side then it will not have an even number on the other”
- draws attn
- Gricean principles of pragmatics: What people mention is more important than what they don’t mention
- Context still has a powerful effect
What did Griggs and Cox (1982) demonstrate in their contextualisation of the Wason selection task?
Better performance for the following concrete examples of Wason selection task:
“If a person is drinking beer, then that person is over 19.”
“Drinking beer” “Drinking coke” “16yo” “22yo”
- Most people checked “beer” and “16yo”.
How does experience affect people’s performance in the Wason selection task?
Johnson-Laird, Legrenzi and Legrenzi (1972): “If a letter is sealed, then it has a 50-lira stamp on it.”
People with postage rule did better, as there was a postage rule around that time - but this example only helps those who used the postage system/country.
Experience appears to be critical - taps into “pragmatic reasoning schemas”
What are pragmatic reasoning schemas?
Sets of generalised, context-sensitive rules defined in relations to classes of goals (e.g. permission, social exchange)
Permission schema: may have these rules
- If a certain action (sealing envelope) is to be taken, then a certain condition (adequate postage) must be met.
- If action is taken, we need to check if that condition was met.
i.e. check if permission has been granted
- If condition wasn’t met, we need to check that the action wasn’t taken.
i.e. check if permission was needed
What is the evolutionary approach to explaining how we respond to the Wason selection task?
Cosmidies (1989): Wason task fits to form of social exchange. “I will do this for you if you do that”
- Evolved to be good aat dealing with these situations?
- Showed that people were good at dealing with Wason selection task when put in form of a social exchange.
What is the problem with Induction?
Even when we draw generalisation from many instances of observation, we can never be completely certain that something is true.
e.g. “Will the sun come up tomorrow?” - seen sun come up many times before, but doesn’t necessarily mean it will come up tomorrow
Can’t make an inductive syllogism that is deductively valid - scandal of philosophy”
Yet, inductive reasoning is the best hypothesis we have to explain the data we observe. Much of our thinking is inductive.
How do we inductively reason?
- Use Analogies: Try to draw conclusions from new observations.
- Reason about causality behind syllogisms
- Test Hypotheses
What is the Wason 246 task? How do people tend to respond? What bias does it reveal in human reasoning?
- Participants asked to find rule that generates a 3 number sequence
- 2-4-6 is a correct sequence - Propose a sequence and experimenter tells you if it is correct or not
- Can announce what you think the rule is and experimenter will tell you if you are correct.
Rule: Increasing numbers
Responses:
Most initially think rule is “sequence increasing by 2” - NO –> surprised.
“6-8-10”, “13-15-17”
Few tried to disconfirm: 1-2-3, 3-2-1
We tend to generate sequences that confirm our hypotheses, and not to disconfirm the rule, when in fact disconfirming the rule may be more important
= Confirmation bias
What is the Confirmation bias?
Bias = tendency to perform in certain way regardless of situation/info given
Confirmation bias = Tendency to only look for info that supports existing beliefs
When confirmation material is removed (so that the task is only categorisation of 2 rules), people do better
What does Klayman and Ha’s (1987) argue about the confirmation bias as a positive test strategy?
Confirmation bias - a positive test strategy, which can be most effective. Depends on rule and environment.
- 2-4-6 task is hard because it penalises strategy, due to rule’s generality
Bias exists because it is often useful, but not guaranteed to work.
