Week 6: Validity pt.2

Question 1

Argument by elimination (valid)

Answer 1

1. Either P or Q
2. Not P
3. Therefore, Q

Question 2

Simplification (valid)

Answer 2

1. P and Q
2. Therefore P

Question 3

Modus Ponens; affirming the antecedent (valid)

Answer 3

1. If P, then Q
2. P.
3. Therefore, Q.

Question 4

Modus Tollens: Denying the consequent (valid)

Answer 4

1. If P, then Q
2. Not Q.
3. Therefore, not P

Question 5

Chain Argument: Conclusion is a conditional (valid)

Answer 5

1. If P, then Q
2. If Q, then R
3. Therefore, If P, then R

Question 6

Equivalence (valid)

Answer 6

1, P if and only if Q
2. Not P.
3. Therefore, not Q

Question 7

Allowing the consequent (invalid)

Answer 7

1. If p, then Q
2. Q.
3. Therefore, P

Question 8

Denying the Antecedent (invalid)

Answer 8

1. If P, then Q.
2. Not P,
3. Therefore, not Q

Question 9

Finding Validity and Invalidity tips

Answer 9

1. Find examples to establish invalidity (counterexamples) - come up with a ase where all the premises are true and the conclusion is false
2. Look for arguments that follow the same pattern, where validity and invalidity may be easier to identify
3. Check for patterns. See if it fits within one of the patterns we learned

Question 10

Semantic Validity

Answer 10

Valid because it follows valid argument form

Question 11

Modal validity

Answer 11

valid because of the meanings of terms.