Which of the following propositions are so related that they cannot both be true, although they can both be false? Choose the correct answer from the options given below.

1.No professors are materialists

2.Some professors are materialists

3.All professors are materialists

4.Some professors are not materialists

A1 and 3 only ✓ Correct

B2 and 4 only

C2 and 3 only

D1 and 4 only

Correct answer: (A) 1 and 3 only

Explanation

'No professors are materialists' and 'All professors are materialists' cannot both be true, yet both can be false.

That condition defines the relation of contrariety.

These two are the E proposition and the A proposition.

On the square of opposition the two universals stand as contraries.

Both fail together if some professors are and some are not materialists.

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