Question

Consider the following argument: If pigs have wings, then pigs can fly. If pigs are lighter than air, then pigs can fly. Pigs have wings or pigs are lighter than air. If pigs have wings or pigs can fly, then pigs don’t have wings. Therefore, donkeys can fly.

(a) Write this argument in symbolic form, using the variables listed below.

Pigs can fly p

Pigs are lighter than air q

Pigs have wings r

Donkeys can fly s

(b) Determine whether the argument is valid or not. Show your working.

Answer 1

a ) If r ⇒ p

If q ⇒ p

r ∪ q

If r∪p ⇒ ¬ r

∴ s

b) The argument is invalid

Explanation:

The argument is invalid because we do not with precision if b), because we do not have enough information about it, and this is because the previous sentences does not mention information about the donkey. We cannot infer something when we do not have enough information.