LSAT "Cannot Be True" Questions: The Inverse Inference
Cannot-be-true questions ask which answer the stimulus rules out. Learn how to flip the inference mindset and avoid the must-be-true trap.
2026-06-01 · 6 min read
How this differs from must-be-true
A "cannot be true" question asks which answer is impossible given the stimulus. Four answers could be true; the credited answer contradicts the facts. It is the mirror image of a must-be-true question, and the trick is keeping the direction straight.
The method
Treat the stimulus as fixed facts. For each answer, ask: could this be true at the same time as everything I was told? If yes, eliminate it. The one answer that cannot coexist with the facts is correct.
Conditional statements are the usual key: if the stimulus says A then B, an answer asserting "A and not B" cannot be true.
Worked example
Stimulus: "Every student who passed the bar took the prep course. No one who skipped the prep course passed."
Answer that cannot be true: "Maria passed the bar but skipped the prep course." This directly contradicts the conditional, so it cannot be true. Other answers — Maria took the course and failed, or took it and passed — are all possible.
Verbloom's conditional diagrams make the contradiction obvious, so you select the impossible answer with confidence.
Frequently asked questions
Is cannot-be-true the same as a must-be-false question?
Yes. Both ask for the answer that the stimulus makes impossible. The four wrong answers are merely possible; the right answer is contradicted by the facts.
Where does the contradiction usually hide?
In a conditional rule. An answer that affirms a sufficient condition while denying its necessary result violates the rule and cannot be true.
How do I avoid mixing this up with must-be-true?
Read the stem carefully and write a quick reminder. For cannot-be-true you are eliminating everything possible and keeping the one impossibility.
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