Which of the following statements are so related that if one of them is true the other must be false, even though both of them can be false?

1.Some adults are far-sighted.

2.No adults are far-sighted.

3.All adults are far-sighted.

4.Some adults are not far-sighted.

A1 & 4 only

B3 & 4 only

C1 & 2 only

D2 & 3 only ✓ Correct

Correct answer: (D) 2 & 3 only

Explanation

Statements 2 and 3 are contraries, so if one is true the other must be false, yet both can be false.

Statement 2, no adults are far-sighted, is the E form.

Statement 3, all adults are far-sighted, is the A form.

A and E stand as contraries on the square of opposition.

Contraries cannot both be true but can both be false.

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