Argument Validity
- What does it mean for an argument to be valid?
- An argument is valid if its conclusion must be true when the premises are true
Validity from Tautologies
- Modus Ponens â if is true, and is true, then must be true
- Modus Tollens â if and is false, then must be false
- Disjunctive Syllogism â if is true, and is false, then is true
- Transitivity of Implication â if and , then
- (and many more)
Valid Argument
- Premise 1 â if it is raining, then the ground is wet
- Premise 2 â it is raining
- Conclusion â the ground is wet
Invalid Argument
- Premise 1 â if it is raining, then the ground is wet
- Premise 2 â the ground is wet
- Conclusion â it is raining