Lesson 5.1: Must-Be-True and Inference Questions

Introduction

In the landscape of the LSAT, logical reasoning is a critical skill that will serve you well not just on the exam, but also in your academic and professional future. This lesson focuses on two of the most common types of logical reasoning questions: must-be-true and inference questions. By mastering these concepts, you will learn to derive conclusions that the stimulus supports fully without overreaching beyond what is presented.

Learning Objectives

• Draw conclusions that the stimulus fully supports and stay within scope.
• Distinguish between must-be-true and most-strongly-supported tasks.
• Select inferences that are guaranteed by the stimulus.
• Reject answers that extend, exaggerate, or reverse the information provided.
• Explain the main ideas and terminology behind must-be-true and inference questions.

1. Understanding Must-Be-True Questions

Must-be-true questions require you to identify an answer choice that must logically follow from the information presented in the stimulus. This means that if the premises of the argument are accepted as true, the conclusion must also be true based on those premises.

1.1 Key Characteristics of Must-Be-True Questions

• Foundation: The conclusions must be directly supported by the text. You are not allowed to make assumptions or introduce new information.
• Question Format: Must-be-true questions often contain phrases such as "which of the following must be true?" or "which statement is supported by the information?"

1.2 Example of a Must-Be-True Question

Stimulus: All cats are mammals. Some mammals are not dogs.

Question: Which of the following must be true?

1. Some cats are not dogs.
2. All mammals are cats.
3. Some mammals are cats.
4. Some mammals are not cats.

Analysis:

Let's analyze the choices:

• Choice 1: Some cats are not dogs.
• This follows directly, as all cats are included in the category of mammals, and not all mammals are dogs. So this must be true.
• Choice 2: All mammals are cats.
• This is incorrect; there are many mammals that are not cats (e.g., dogs, rabbits).
• Choice 3: Some mammals are cats.
• This follows from the stimulus but is not a definitive conclusion since we cannot assume any mammal is a cat without additional information.
• Choice 4: Some mammals are not cats.
• This is true, but it does not follow as a direct consequence of the premises either; thus, it is less direct than Choice 1.

The correct answer is Choice 1. It is the only statement that logically flows from the stimulus, showing a concrete example of how to pick must-be-true conclusions based purely on given statements.

2. Understanding Inference Questions

Inference questions, similar to must-be-true questions, require you to derive a conclusion from the information provided. However, inference questions allow a slight degree of interpretation, which can sometimes lead to ambiguity.

2.1 Key Characteristics of Inference Questions

• Flexibility: While the answer must connect to the stimulus, it can be a slight inference rather than a direct conclusion.
• Question Format: Inference questions are often worded with phrases such as "which of the following can be inferred from the statements?"

2.2 Example of an Inference Question

Stimulus: If it rains tomorrow, I will stay indoors.

Question: Which of the following can be inferred?

1. I will not go outside if it rains tomorrow.
2. It might rain tomorrow.
3. I will stay indoors.

Analysis:

Let's evaluate each choice:

• Choice 1: I will not go outside if it rains tomorrow.
• This is indeed a logical inference from the stimulus.
• Choice 2: It might rain tomorrow.
• This is not guaranteed; the passage gives no evidence of the likelihood of rain.
• Choice 3: I will stay indoors.
• This is a valid inference but only completely accurate if we assume it does rain. Thus, it is not definite without that condition.

The best answer here is Choice 1 because it directly reflects the conditional nature of the information provided.

3. Distinguishing Must-Be-True from Most-Strongly-Supported

While must-be-true questions require definitive conclusions based on the text, most-strongly-supported questions allow for conclusions that are likely based on the information given, thus creating a nuanced difference between the two.

3.1 Key Distinctions

• Scope of Support: Must-be-true answers rely strictly on the information provided, whereas most-strongly-supported answers can incorporate a wider interpretation of the stimulus.
• Certainty Levels: Must-be-true reflects absolute certainty if the premises hold, while most strongly supported indicates high likelihood but does not guarantee definitive truth.

3.2 Worked Example of Distinction

Stimulus: Studies show that students who study in groups often score higher on exams than those who study alone.

Must-be-True Question: Which of the following must be true?

• A. Studying in groups leads to higher scores.
• B. Students who study alone will score lower.
• C. All students benefit from group study sessions.

Answer Analysis:

• Choice A may sound reasonable but cannot be assumed without additional evidence establishing causation.
• Choice B: This cannot be definitively concluded from the stimulus as correlation isn't causation.
• Choice C: This overreaches as it claims all students benefit without supporting evidence.

No answer choice for this scenario must absolutely be true based only on the stimulus provided. However, in contrast, a most-strongly-supported question might ask which statement is likely based on the findings, allowing for broader conclusions.

Conclusion

Navigating through must-be-true and inference questions is essential for excelling in the logical reasoning section of the LSAT. By understanding the distinctions and practicing the concepts of drawing supported conclusions without overreaching, you will refine your skills and approach to these common types of questions.

Study Notes

• Must-be-true answers must reflect information directly from the stimulus.
• Inference questions allow interpretations but must also be supported by the stimulus.
• Distinguish between must-be-true (absolute certainty) and most-strongly-supported (likely conclusions).
• Practice careful reading of each question, looking for linguistic cues and logical connections.
• Identify answer tendencies—beware of exaggerations or assumptions in answer choices.