LSAT Must Be True Questions Practice Questions with Answers

Logical reasoning sections on the Law School Admission Test (LSAT) include a high volume of inference-based tasks, where success depends on identifying the single statement that is logically guaranteed by the provided text. LSAT Must Be True questions account for approximately 10-15% of the Logical Reasoning section, making them a cornerstone of a high score. Unlike other question types that ask you to strengthen an argument or find a flaw, these questions require you to treat the stimulus as a set of facts and find the one answer choice that cannot be false if those facts are true.

Concept Explanation

LSAT Must Be True questions are logical inference tasks that require you to identify a statement that is a 100% certain consequence of the premises provided in the stimulus. These questions do not contain an argument with a conclusion and supporting evidence; instead, they present a set of statements that you must accept as absolute truth. Your goal is to find the answer choice that is proven by the stimulus, often through the application of formal logic, conditional reasoning, or the combination of multiple facts. Common prompts include "Which one of the following must be true?" or "Which one of the following can be properly inferred from the passage?" To succeed, you must avoid "could be true" answers—statements that are possible but not guaranteed—and "exaggerated" answers that go beyond the scope of the evidence.

Effective preparation involves utilizing a comprehensive LSAT Prep strategy that emphasizes formal logic. You should look for "linkable" statements, such as conditional chains where $A \rightarrow B$ and $B \rightarrow C$, allowing you to infer $A \rightarrow C$. Additionally, paying close attention to quantity indicators like "some," "most," and "all" is vital, as these terms define the boundaries of what can be proven. For those looking to refine their skills across different standardized tests, comparing these logical structures to hard GRE reading practice test practice questions can reveal how inference logic remains consistent across graduate-level exams.

Solved Examples

1. Example 1: Conditional Logic

   Stimulus: If a city has a professional sports team, it must have a stadium. Centralia does not have a stadium.

   Solution:

   1. Diagram the first statement: $\text{Sports Team} \rightarrow \text{Stadium}$.
   2. Identify the contrapositive: $\text{No Stadium} \rightarrow \text{No Sports Team}$.
   3. Apply the fact: Centralia has no stadium.
   4. Conclusion: Centralia does not have a professional sports team.

2. Example 2: Overlapping Quantifiers

   Stimulus: Most residents of Oak County are homeowners. Some residents of Oak County are avid gardeners.

   Solution:

   1. Recognize that "most" means more than 50%.
   2. Recognize that "some" means at least one.
   3. Consider the overlap: While it is possible all gardeners are homeowners, it is not guaranteed. However, if the stimulus said "Most residents are homeowners AND most residents are gardeners," then at least one person must be both.
   4. In this specific case, the only thing that must be true is that there is at least one resident of Oak County who is a homeowner or a gardener. Note: Be careful not to infer that some homeowners are gardeners unless the numbers force an overlap.

3. Example 3: Causal Combinations

   Stimulus: Every employee who attended the seminar received a certificate. Sarah is an employee who did not receive a certificate.

   Solution:

   1. Diagram the rule: $\text{Attended Seminar} \rightarrow \text{Received Certificate}$.
   2. Identify the contrapositive: $\text{No Certificate} \rightarrow \text{Did Not Attend Seminar}$.
   3. Apply Sarah's situation: She did not receive a certificate.
   4. Conclusion: Sarah did not attend the seminar.

Practice Questions

1. All successful entrepreneurs possess a high degree of resilience. Some resilient people are not interested in financial gain. No person who is uninterested in financial gain will ever start a major corporation.

2. If the temperature drops below freezing, the water pipes in the basement will burst. If the water pipes in the basement burst, the house will flood. The house did not flood.

3. Most students at Westview High School participate in extracurricular activities. Every student who participates in extracurricular activities must maintain a 3.0 GPA. Some students who maintain a 3.0 GPA are also members of the National Honor Society.

4. No one who is a member of the chess club is also a member of the wrestling team. All members of the wrestling team are required to attend daily weightlifting sessions. Mark is a member of the chess club.

5. Any painting by Monet is considered an Impressionist masterpiece. Some Impressionist masterpieces are currently held in private collections. All paintings in the Miller collection are by Monet.

6. Whenever the local economy enters a recession, the unemployment rate rises. If the unemployment rate rises, consumer spending decreases. Last year, consumer spending in the local economy did not decrease.

7. Most of the books on the top shelf are biographies. None of the biographies on the top shelf were written before 1950. Some of the books on the top shelf are bound in leather.

8. All tropical fish require warm water to survive. No fish that requires warm water can live in the Arctic Ocean. A Gold-Spotted Tang is a type of tropical fish.

Answers & Explanations

1. Answer: Some resilient people do not start major corporations.
   Explanation: The stimulus states some resilient people are not interested in financial gain, and those uninterested in financial gain will never start a major corporation. Combining these two facts proves that there exists at least one resilient person who will not start a major corporation.
2. Answer: The temperature did not drop below freezing.
   Explanation: This follows a chain: $\text{Freezing} \rightarrow \text{Burst Pipes} \rightarrow \text{Flood}$. The contrapositive is $\text{No Flood} \rightarrow \text{No Burst Pipes} \rightarrow \text{Not Freezing}$. Since the house did not flood, the temperature could not have dropped below freezing.
3. Answer: Most students at Westview High School maintain a 3.0 GPA.
   Explanation: We know most students do extracurriculars, and all extracurricular students have a 3.0 GPA. Therefore, that "most" group must all have a 3.0 GPA, ensuring that most students at the school meet that criteria.
4. Answer: Mark is not required to attend daily weightlifting sessions as a member of the wrestling team.
   Explanation: Since Mark is in the chess club, and no chess club member is on the wrestling team, Mark is not on the wrestling team. While he could go to the gym, he is not required to do so by the wrestling team mandate.
5. Answer: All paintings in the Miller collection are Impressionist masterpieces.
   Explanation: The stimulus says $\text{Monet} \rightarrow \text{Impressionist}$. It then says all Miller paintings are Monet. Therefore, by transitive property, all Miller paintings are Impressionist masterpieces.
6. Answer: The local economy did not enter a recession last year.
   Explanation: The logical chain is $\text{Recession} \rightarrow \text{Unemployment Rises} \rightarrow \text{Spending Decreases}$. Since spending did not decrease, we work backward through the contrapositives to conclude no recession occurred.
7. Answer: There is at least one book on the top shelf that was not written before 1950.
   Explanation: Since most books on the shelf are biographies, and none of those biographies were written before 1950, there must be at least one book (specifically, any of those biographies) that was not written before 1950.
8. Answer: A Gold-Spotted Tang cannot live in the Arctic Ocean.
   Explanation: The chain is $\text{Gold-Spotted Tang} \rightarrow \text{Tropical Fish} \rightarrow \text{Warm Water} \rightarrow \text{Not Arctic}$. Thus, the Tang cannot survive in the Arctic.

Frequently Asked Questions

What is the difference between "Must Be True" and "Most Strongly Supported"?

Must Be True questions require an answer that is logically guaranteed (100% certainty), whereas Most Strongly Supported questions seek the answer choice that is most likely to be true based on the evidence, even if it isn't strictly proven. While the approach is similar, the standard of proof is slightly lower for Most Strongly Supported questions.

Can I use outside knowledge to answer LSAT Must Be True questions?

No, you should never use outside knowledge; you must rely exclusively on the information provided in the stimulus. Even if a statement is factually true in the real world, it is a wrong answer if it cannot be proven by the specific text provided on the exam.

How do I identify a Must Be True question?

Look for stems that use words like "must," "inferred," "follows logically," or "properly concluded." These indicate that the answer choice is a necessary consequence of the premises.

What are the most common traps in these questions?

Common traps include "Could Be True" answers, which are possible but not certain, and "Exaggerated" answers, which take a premise about "some" people and apply it to "all" people. Always check the strength of the language in the answer choice against the strength of the language in the stimulus.

Should I diagram every Must Be True question?

You should only diagram questions that contain conditional "if-then" statements or formal logic quantifiers like "all," "none," or "only if." For stimuli that are more informal or fact-based, a careful mental summary is often more efficient than a formal diagram.

How can I practice these effectively?

Consistent practice with an AI Exam Simulator can help you recognize patterns in logical inferences. By reviewing detailed explanations, you can learn to distinguish between a valid inference and a common logical fallacy.