LSAT Must Be True / Inference

What It Is

Must Be True questions do not present a flawed argument. The stimulus is a set of facts, and you must identify which answer is guaranteed to be true based solely on those facts. The key word is MUST -- not could be, not probably is.

How to Identify the Question Type

• Which of the following can be properly inferred from the statements above?
• If the statements above are true, which of the following must also be true?
• The statements above most strongly support which of the following?

Attack Strategy

• Step 1: Read the stimulus as a list of facts, not an argument -- there is no flaw to find
• Step 2: Note key logical relationships: if/then, all, some, none, most, percentages
• Step 3: The correct answer should follow necessarily -- it should feel close to obvious
• Step 4: Eliminate answers that go beyond what the facts guarantee
• Step 5: Be especially alert to conditional logic and contrapositives

Conditional Logic Guide

If the stimulus says 'All A are B,' you can infer: (1) If something is A, it is B. (2) If something is NOT B, it is NOT A (contrapositive). You CANNOT infer: All B are A. This is the most common trap on MBT questions.

Example Problem

Stimulus: 'All students who passed the bar exam completed the ethics course. Some students who completed the ethics course attended the prep seminar.' Must Be True: Some students who passed the bar exam completed the ethics course. CANNOT infer: All students who completed the ethics course passed the bar exam.

Common Wrong Answer Traps

• Answers that are plausible or likely but not guaranteed by the facts
• Answers that reverse the direction of a conditional statement
• Answers that import outside information not stated in the stimulus

Top Tips

• If an answer requires any assumption beyond the stimulus, eliminate it
• 'Most' does not mean all -- be precise about what quantifiers guarantee
• The correct answer often feels too obvious -- that is usually a good sign