Contrapositive
GMAT glossary · Verbal Reasoning
Definition
The logically equivalent form “If not B, then not A” of the conditional “If A, then B.” Unlike the converse or inverse, the contrapositive is always logically equivalent to the original conditional, making it the only safe rephrasing for valid deductive inference on the GMAT.
Contrapositive in plain English
The contrapositive is a 'flip and negate' rewrite of an if...then statement that means EXACTLY the same thing as the original, so it's always safe to use. Start with 'If it's a dog, then it's an animal'; the contrapositive is 'If it's NOT an animal, then it's NOT a dog,' which is obviously just as true. The trick is you swap the two parts AND negate both. Beware two look-alikes that are NOT safe: the converse ('If B then A') and the inverse ('If not A then not B') can be false even when the original is true, which is exactly the trap the GMAT sets.
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