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

Question

Quizplus · Accepted Answer

An indirect proof (also known as proof by contradiction) involves assuming the negation of the conclusion and showing that this assumption leads to a contradiction. The conclusion of the given argument is (∃x)Sx, so the appropriate assumption for an indirect proof is its negation, which is ∼(∃x)Sx.

1. (∃X)Qx ⊃ (∀X)(Rx ⊃ Sx)