Simple Guide on Must be True and Must be False Questions

Intro to Must be True (MBT) and Must be False (MBF) Questions

This blog is a part of the “Approach Question Type” series and like all articles in this series will focus on step 4 of the “Analyze Stimulus” step. If you need a refresher on how to approach LR questions generally, make sure to check up on our blog "How to Approach the Logical Reasoning Section.”

‍Table of Contents:

• What is a MBT/MBF Question?
• Question Stems
• Trap Answer Choices
• Approach
• Step-by-step Answers Passthrough

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What is a MBT/MBF Question?

MBF/MBT questions test our ability to identify valid, invalid, and doubtful statements. 

"Must Be True" (MBT) questions ask you to identify the statement that is logically guaranteed based on the information provided in the passage or argument. These questions require you to choose the option that must logically follow from the premises. The correct answer must be a statement that is guaranteed to be true if the premises in the passage are true. The answer should be a logical consequence of the information given, not just a plausible or likely outcome.

In contrast, "Must Be False" (MBF) questions ask you to identify the statement that cannot be true given the information in the passage or argument. These questions require you to choose the option that contradicts or cannot be supported by the provided information.

MBT and MBF depend on our formal logic skills. That is, to find the correct answer, we must depend solely on our ability to discern the validity of an argument or statement, without making any assumptions. 

Question Stems

MBT Question Stems:

1. "If all of the statements above are true, which of the following statements must logically follow?"
2. “If the statements above are true, which one of the following is an inference that can be properly drawn on the basis of them?”
3. "According to the passage, which of the following statements is necessarily true?"
4. "Which of the following can be properly inferred from the passage?"
5. "Based on the passage, which of the following is a valid deduction?"

MBF Question Stems:

1. "If all of the statements above are true, which of the following statements cannot be true?"
2. "Which of the following must be false given the facts in the passage?"
3. "Based on the passage, which of the following is definitely false?"
4. "Which of the following conclusions contradicts the passage?"
5. "Which of the following statements is inconsistent with the information provided in the passage?"

Trap Answer Choices: 

Trap answer choices are designed to be plausible but ultimately incorrect. Let’s quickly review some common types alongside a passage:

Passage: Consuming a variety of fruits and vegetables is essential for maintaining overall health. These foods provide critical vitamins, such as vitamin C and iron, and contain fiber that aids in digestion. While other food groups are also important to fulfill nutrient requirements, a diet lacking in fruits and vegetables may lead to nutrient deficiencies and compromised health in some critical vitamins.

1. Extreme Statements — Choices that go too far beyond the information provided. some text
   1. Trap Answer: "Eating only fruits and vegetables will guarantee perfect health and prevent all diseases."
   2. Explanation: This choice is too extreme. The passage suggests that fruits and vegetables are important for health, but it doesn’t claim that they can prevent all diseases or guarantee perfect health. It extends the evidence too far.
2. Out of Scope — Choices that introduce information not covered in the passage or question.some text
   1. Trap Answer: "A diet high in protein is more beneficial than one rich in carbohydrates."
   2. Explanation: This choice introduces a comparison that isn’t discussed in the passage. The passage focuses on fruits and vegetables, not protein vs. carbohydrates. This statement could be true or false; we don’t have the necessary information in the stimulus to decide.
3. Misinterpretations: Choices that misinterpret the passage’s argument or evidence. some text
   1. Trap Answer: "Consuming fruits and vegetables is sufficient for a balanced diet."
   2. Explanation: This choice misinterprets the passage. The passage emphasizes the importance of fruits and vegetables but does not claim they are sufficient on their own for a balanced diet. We might need to include certain protein, fat, and carbohydrate sources.
4. Half-True Statements: Choices that include some true elements but fail to fully capture the passage’s meaning. some text
   1. Trap Answer: "Including fruits and vegetables in your diet is important because they are the only sources of essential vitamins."
   2. Explanation: While it's true that fruits and vegetables are important sources of vitamins, the passage likely does not claim they are the only sources.
5. Irrelevant Evidence: Choices that present evidence that doesn’t support the claim or argument in the passage. some text
   1. Trap Answer: "People who eat fruits and vegetables daily are also more likely to exercise regularly."
   2. Explanation: This may or may not be true, but it’s irrelevant to the argument made in the passage about the importance of fruits and vegetables for obtaining vitamins and minerals.
6. Overgeneralizations: Choices that generalize beyond what’s stated or implied in the passage. some text
   1. Trap Answer: "A balanced diet should include only fruits and vegetables."
   2. Explanation: This answer overgeneralizes the passage's recommendation by suggesting that fruits and vegetables are the only necessary components of a balanced diet, which the passage likely doesn’t claim.

Approach 

Now that we are aware of some common traps, next up is to find the correct answer choice. To analyze and find the correct answer choice begins with the stimulus. Do not make outside assumptions or inferences for MBF/MBT questions. Everything we know and can know is contained in the stimulus. 

Because MBF/MBT questions are formal logic questions, we want to be extra attentive to any conditional or causal logic in the stimulus. Can we diagram out any formal logic conditional chains? Are there contrapositives that we can make to help us gain more information? 

We must decipher the validity of the provided statements in order to find the correct answer choice. For MBF/MBT questions, the Truth Spectrum below can help us to confidently visualize and determine the correct answer choice. If it is helpful for you to draw this out really quickly, you are welcome to do so on your scrap paper while doing the LSAT. 

TRUTH SPECTRUM

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The Truth Spectrum is rather straightforward. As you approach the answer choices in MBF or MBT questions, you plot each answer on the spectrum. For each answer choice, we must ask ourselves what is valid and true, and what is only “likely” or “unlikely” to be true? Just because a statement might be well supported, doesn’t mean it must be true. Contrastingly, just because a statement has no support or weak support, doesn’t necessarily prove it must be false. The common answer traps, and most statements in the LSAT and in life have some level of doubt; so be careful of labeling answer choices as absolutes. If there is still reasonable doubt or room for otherwise, then we cannot confidently plot that answer choice as a “Must”. If you do put a statement on either end of the spectrum while looking through the answers, you should be able to pinpoint with certainty what piece(s) of information lead you to claim so.

Step-by-step Answers Passthrough

As you go through each answer choice, this can be a quick helpful guide.

1. Is this statement / piece of information relevant and within the scope of the stimulus? 
2. What makes me want to believe or disbelieve this statement? Can I pinpoint the evidence or support? Is there even evidence? 
3. Plot the statement on the truth spectrum. 
4. If MBF or MBT, can you pinpoint the formal logic presented? Is there truly no room for doubt?some text
   1. Probable and strongly supported does NOT necessarily mean must be true.
   2. Improbable or non-evidence isn’t necessarily cannot be true.

Mastering MBT and MBF questions on the LSAT involves a precise understanding of logical relationships and careful evaluation of answer choices. The Truth Spectrum isn’t going to magically help you find the answer correctly right away, but it can be used for these question types to force you to analyze with the right mindset — to ask yourself constantly which statements must be true or false, or could be true/false based on the information provided. 

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