Lecture_08_Reasoning & Problem Solving Flashcards
Formal Rules of Logic
- Deductive reasoning
- Inductive reasoning
- Conditional reasoning
Reasoning
Drawing conclusions by putting statements (premises) together using logic
1) to make sense of our present experiences and ideas, and to plan for the future
2) to establish and verify facts
Premise
Statement of fact that is assumed to be true
Deductive Reasoning
- Top-down reasoning”
- If the premises are true, the conclusion must also be true.
- Premise 1: All cognitive processes involve brain activities.
- Premise 2: Memory is a cognitive process.
- Conclusion: Memory involves brain activities.
The Problem of Deductive Reasoning
- What’s important is the form of the argument
- The truth of the premise in the real world & your prior knowledge are irrelevant!
- Premise 1: All birds have wings.
- Premise 2: Unicorns are birds. (?)
- Conclusion: Unicorns have wings.
Inductive Reasoning
Bottom-up reasoning
- If the premises are true, the conclusion is also LIKELY to be true.
- Premise 1: Restaurant A has many delicious dishes.
- Premise 2: You order an omelet.
- Conclusion: The omelet is delicious.
The Problem of Inductive Reasoning
The conclusion is likely, but it’s NOT guaranteed to be true.
- Based on probability.
- 80% of brain surgeons are men.
- Lee is a brain surgeon.
- Lee is a man.
Conditional Reasoning
If P-then Q
- Deductive reasoning that involves conditional statements
- Premise 1: If P, then Q
- Premise 2: A statement about whether P or Q is true or not true
- Conclusion: A statement about whether P or Q is true or not true
2 Valid Forms of Conditional Reasoning
- Affirming the antecedent (modus ponens)
- Denying the consequence (modus tollens)
Premise 1: If P, then Q
Premise 2: P
Conclusion: Q
- Valid
- Affirming the antecedent
- Modus ponens
Premise 1: If P, then Q
Premise 2: Q
Conclusion: P
- Invalid
- Affirming the consequence
Premise 1: If P, then Q
Premise 2: ~P
Conclusion: ~Q
- Invalid
- Denying the antecedent
Premise 1: If P, then Q
Premise 2: ~Q
Conclusion: ~P
- Valid
- Denying the consequence
- Modus tollens
Wason’s Card Selection Task
- 4 cards
- Each card has two sides: a letter and a digit.
- Rule: If a vowel is on one side, there is an even number on the other side
- Try to confirm this rule by turning over the fewest number of cards
Why do participants make mistake in Wason’s Card Selection task?
People make mistakes by seeking verification rather than falsification
Logical Fallacies
- Begging the question
- After this, therefore because of this
- Ad hominem
- Slippery slope