1. (∀x)(Px ⊃ Qx)
2. ∼(∃x)[(Px • Rx) • Qx]
3. (∃x)Rx / ∼(∀x)Px
-Which of the following propositions is an appropriate assumption for an indirect proof of the conclusion of the given argument?
A) ∼Px
B) ∼(∀x)∼Px
C) Px
D) (∀x)Px
E) ∼(∀x)Px

Question

Quizplus · Accepted Answer

To prove ∼(∀x)Px indirectly, assuming the opposite of what you want to prove is a standard approach. Here, assuming (∀x)Px (D) is the opposite of the conclusion ∼(∀x)Px, making it the appropriate assumption for an indirect proof.

1. (∀X)(Px ⊃ Qx)