Question

Which argument below is deductively valid?
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a
If Ralph has fur, then Ralph is a dog. Ralph is a dog. So, Ralph has fur.

b
If Ralph has fur, then Ralph is a dog. Ralph is not a dog. So, Ralph does not have fur.

c
Ralph is not a dog. All dogs bark. So, Ralph does not bark.

d
All dogs wag their tails. Ralph wags his tail. So, Ralph is a dog.

Answer 1

b

Form: If P then Q; not Q; therefore not P. (Modus tollens — a valid deductive form.)