Which of the following statements are correct about sub-contrary propositions? Choose the correct answer from the options given below.

1.If one is true, the other must be false

2.They cannot both be false

3.If one is false, the other must be true

4.They can both be true

A1 and 3 only

B2, 3 and 4 only ✓ Correct

C1, 2 and 3 only

D1 and 4 only

Correct answer: (B) 2, 3 and 4 only

Explanation

Sub-contraries cannot both be false, though they can both be true.

The I and O propositions are sub-contraries in the square of opposition.

Statement 2 states that they cannot both be false.

Statement 3 states that if one is false the other must be true, which follows from that.

Statement 4 states that they can both be true, as when some are and some are not.

What fails is any demand that one's truth force the other's falsity.

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