If the statement "Some animals are birds" is given as false then which of the following statements can be immediately inferred to be false?
All animals are birds.
Concept: On the Square of Opposition, the universal affirmative (A) 'All S are P' and the particular affirmative (I) 'Some S are P' stand in a relation of subalternation: the truth of A implies the truth of I. Equivalently, if I is false, then A must also be false, because a universal claim cannot hold when even its weaker particular version fails.
Working: We are told 'Some animals are birds' (an I-proposition) is false. Since 'All animals are birds' (the corresponding A-proposition) would, if true, force 'Some animals are birds' to be true, the falsity of the I-statement immediately makes the A-statement false as well. Therefore 'All animals are birds' can be immediately inferred to be false.
Why the other choices are wrong:
'No animals are birds' is the contradictory of the false I-statement, so it must be true, not false.
'Some animals are not birds' is the E/O-region result that also follows as true when 'Some animals are birds' is false, so it cannot be the false one.
'Some birds fly' involves an entirely different predicate (flying) and is not logically connected to the given proposition, so its truth value cannot be inferred at all.
Takeaway: If a particular affirmative is false, its corresponding universal affirmative is necessarily false.
Correct answer: All animals are birds.
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