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Must Be True & Cannot Be True Questions

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Must Be True & Cannot Be True Questions

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Must Be True & Cannot Be True Questions — Key Facts for LSAT India Core concept: Must Be True = what MUST be true if the passage is true; Cannot Be True = what CANNOT possibly be true given the passage High-yield point: For Cannot Be True questions, 4 of 5 answers will be possible — you only need to find the one that contradicts the passage ⚡ Exam tip: Use the negation test — negate each answer and ask if the passage could still be true; if yes, it’s not a Must Be True

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Must Be True & Cannot Be True Questions — LSAT India Study Guide

The Precision of Must Be True Questions

Must Be True questions are among the most common and most precisely logical question types on LSAT India RC. They require you to identify the answer choice that is most firmly supported by the passage — the one that must be true if every statement in the passage is accepted as true.

The word “must” is critically important. This is not asking what is probably true, likely true, or often true. It is asking what is necessarily true — what you can state with logical certainty based on the passage alone.

This precision makes Must Be True questions somewhat unique among RC types: they are closer to formal logic than to reading comprehension. You need to think in terms of logical necessity, not general plausibility.

Identifying Must Be True Questions

Watch for these question stems:

  • “Which of the following must be true based on the passage?”
  • “It can be inferred from the passage that…”
  • “If the statements in the passage are true, which of the following must also be true?”
  • “The passage most strongly supports which of the following conclusions?”
  • “Which of the following is most completely supported by the passage?”

Note: “It can be inferred” and “must be true” are functionally equivalent on the LSAT. Both ask for what necessarily follows from the passage.

Identifying Cannot Be True Questions

Watch for these question stems:

  • “Which of the following cannot be true based on the passage?”
  • “Which of the following statements is most clearly contradicted by the passage?”
  • “Each of the following could be true EXCEPT:”
  • “Which of the following is inconsistent with the passage?”

On “EXCEPT” questions (formally called “Must Be True EXCEPT”), four of the five answer choices must be true based on the passage, and one cannot be true. You must identify the one that is NOT supported.

The Logical Framework: Necessary vs. Sufficient

Understanding the distinction between necessary and sufficient conditions is essential for Must Be True questions:

A sufficient condition: If X is true, then Y is definitely true. X guarantees Y.

  • Example: If it is raining, then it is cloudy. Being rainy is sufficient for being cloudy.

A necessary condition: If Y is true, then X must be true. Y cannot be true without X.

  • Example: Being alive is necessary for being human. Everything that is human is alive.

In LSAT Must Be True questions, you are typically asked about necessary conditions — what must be the case given the passage. If the passage says “X is sufficient for Y,” you can infer that “if X is true, Y is true” (must be true). But you cannot infer that “if Y is true, X is true” (that does not follow).

Watch carefully for whether the passage describes a sufficient or a necessary condition — confusing them is one of the most common sources of errors on these questions.

A Worked Must Be True Example

Passage:

“A recent study examined the relationship between sleep duration and academic performance among university students. The researchers found that students who slept less than six hours per night scored, on average, 12% lower on standardized exams than students who slept seven to eight hours. Students who slept more than nine hours per night also scored lower, though by a smaller margin. The researchers controlled for variables including prior academic achievement, course load, and socioeconomic status.”

Question: “It can be inferred from the passage that the researchers would most likely agree with which of the following?”

Evaluating answer choices:

(A) “All students who sleep less than six hours will perform poorly on exams.” Cannot be inferred. The passage says students who slept less than six hours scored 12% lower on average. Averages do not apply to every individual. This overgeneralizes the data.

(B) “Sleep duration is an important factor in academic performance.” This is a reasonable inference. The researchers conducted a controlled study to examine the relationship, suggesting they believe sleep duration affects academic performance. While the passage does not use the word “important,” the fact that they controlled for multiple variables and reported significant findings implies they consider sleep duration a meaningful factor.

(C) “Students who sleep between seven and eight hours perform better than students who sleep more than nine hours.” Cannot be inferred. The passage says students sleeping more than nine hours also scored lower, but it does not compare the seven-to-eight hour group directly to the more-than-nine-hour group.

(D) “If a student improves their sleep habits, their academic performance will necessarily improve.” Cannot be inferred. The study shows a correlation (association), not causation. We cannot conclude that changing sleep habits will cause improved performance.

Correct answer: (B)

A Worked Cannot Be True Example

Passage:

“The city council has proposed two measures to address traffic congestion. Measure A would expand the public transit system by adding three new subway lines. Measure B would implement congestion pricing — charging drivers a fee to enter the city’s densest areas during peak hours. Transit experts estimate that Measure A would reduce vehicle traffic by 8–10%. Economic analysts project that Measure B would reduce traffic by 15–20%. Both measures would require significant public investment.”

Question: “Which of the following cannot be true based on the passage?”

(A) “Measure B would reduce traffic more than Measure A would.” This CAN be true — the passage explicitly says Measure B would reduce traffic by 15–20% while Measure A would reduce it by 8–10%. 15–20% is more than 8–10%. Cannot be eliminated.

(B) “Only one of the two measures would be implemented.” This CAN be true — the passage describes both measures as proposals, with no indication that both must be implemented simultaneously. It is possible that only one is adopted.

(C) “Both measures would require public investment.” This MUST be true — the passage explicitly states “Both measures would require significant public investment.” Cannot be the answer (we need what CANNOT be true).

(D) “Measure A would reduce traffic by more than 20%.” This CANNOT be true. The passage says Measure A would reduce traffic by only 8–10%. More than 20% contradicts the passage directly. The correct answer is (D).

The Negation Test for Must Be True

The most powerful technique for Must Be True questions is the negation test. Here is how it works:

For each answer choice, temporarily assume the negation of the statement. Then ask: “If I assume this negation, does the passage still make sense, or does the passage break down?”

  • If the passage can still be fully true with the negation assumed, the original statement is NOT a Must Be True.
  • If the passage cannot be fully true with the negation assumed, the original statement IS a Must Be True.

Example: Passage: “All roses are flowers. Some flowers are red.”

Test answer: “Some roses are flowers.” Negation: “No roses are flowers.” Can the passage still be true? No — “All roses are flowers” would be contradicted. Therefore, “Some roses are flowers” must be true. It passes the negation test.

Test answer: “Some roses are red.” Negation: “No roses are red.” Can the passage still be true? Yes — the passage says some flowers are red, but does not say any roses are red. Therefore, “Some roses are red” is not a Must Be True.

Common Must Be True Patterns

  • Combining two premises: If the passage says “All X are Y” and “All Y are Z,” you can infer “All X are Z.”
  • Substituting definitions: If the passage defines a term in a specific way, and then applies that term, you can infer the implications of that definition.
  • Partial support for a broader claim: If the passage provides evidence for a conclusion but also acknowledges limitations, you can infer the more modest claim that is fully supported.
  • Tone-based inferences: If the passage’s language is critical, you can infer that the author does not endorse the position being described.

Common Cannot Be True Patterns

  • Direct contradiction: The answer choice states the opposite of what the passage explicitly says.
  • Overgeneralization from a sample: The passage describes a specific group, and the answer applies that group’s characteristics to a broader population.
  • Conflating correlation and causation: The passage describes a correlation, and the answer treats it as a causal relationship.
  • Inconsistent with passage-defined terms: The answer attributes a property to something that the passage defines as not having that property.

Exam Strategy Summary

  • Must Be True: Use the negation test. Find the answer that, if negated, would make the passage impossible or incoherent.
  • Cannot Be True: Confirm that four answers CAN be true (are consistent with the passage) and one definitely CANNOT. Eliminate the four that are possible.
  • Always work from the passage, never from outside knowledge: If the passage does not state or imply it, it cannot be a Must Be True inference.
  • Watch for answer choices that are too strong: Words like “all,” “always,” “never,” and “must” in answer choices often signal that the answer overstates what the passage supports.
  • Distinguish inference from summarization: A Must Be True answer is not just a restatement of what the passage says — it is something new that follows from what the passage says.

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