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The big question types · Lesson 9 of 14

Must be true questions

After this lesson, you can identify must be true question stems, apply the right reasoning structure to the stimulus, and eliminate the 5 most common wrong answer patterns before you choose.

5 min video, plus notes and 1 practice question below

In this lesson

• Recognize the exact stem phrases that signal a must be true question
• Apply conditional logic, comparative reasoning, and causal reasoning to find what's guaranteed
• Spot the 5 wrong answer patterns test writers use to bait you
• Predict your own answer before you read the choices
• Confirm your final choice against the stimulus before you lock it in

How to spot a must be true question

Must be true questions show up constantly on LSAT logical reasoning, and once you know the pattern, they get a lot more manageable, even the tricky ones. You'll spot them by their stem. Look for phrasing like "which one of the following must also be true," "what can be properly inferred based on the information above," and "what follows logically from the statements above." The wording shifts from question to question, but the task underneath stays the same.

Every one of these stems asks you to find what must be true based only on the given information. That means no guessing and no outside assumptions. You want to know what's guaranteed by the stimulus, not anything you'd add from real world knowledge or common sense.

The 3 reasoning structures behind these questions

3 reasoning structures show up again and again in must be true stimuli. The first is conditional logic: if A requires B, and B requires C, then A requires C. This kind of if-then chain is now more common on LSAT logical reasoning since logic games no longer gets tested, so more conditional reasoning has moved into this section. Your job is to trace the connections between the statements and work out what they force to be true.

The second structure is comparative reasoning, where you're weighing one group against another and paying attention to the numbers underneath. A small percentage can still describe a huge number, and a large percentage can still describe a tiny one. Test writers like to build comparisons that sound supported but actually go further than the stimulus allows.

The third structure is causal reasoning built from a chain of conditional statements. It shows up less often, but each link in the chain lets you infer the final outcome, the same way the A requires B requires C example works for conditional logic. This link by link approach works because each statement guarantees the next one, so once you accept the first link, the final outcome is locked in whether or not the stimulus spells it out directly.

5 wrong answer patterns to watch for

Test writers write 5 wrong answer patterns into must be true questions on a regular basis. The first is scope: an answer choice that introduces a new term or concept the stimulus never supported. The second is an unsupported relationship, one that connects 2 ideas or builds on logic the stimulus doesn't actually back up.

Third, watch for reversals and negations, where a choice improperly flips or negates a conditional or causal relationship from the stimulus. Fourth, some choices overreach, making a claim stronger than anything the stimulus supports. Fifth, a choice can directly contradict what the stimulus told you. Cross those off fast, but read carefully. A single word can flip the whole meaning of a choice, so give every word a close look before you decide.

This matters most with reversals and negations. Swapping one term for its opposite, or moving a "not" onto the wrong condition, can turn a choice that sounds right into a trap in an instant, so slow down on any choice that echoes the stimulus almost word for word.

The step by step method

Put it together and you get a 5 step method. First, ID the question type by spotting phrases like "must be true" or "can be inferred." Second, analyze the stimulus: break down each piece of information, link related terms together, and identify which reasoning structure, conditional, comparative, or causal, is at work.

Third, predict or prephrase your own answer before you look at the choices. Fourth, knock out any choice that matches one of the 5 trap patterns. Fifth, double check your remaining choice against the stimulus, confirming it's fully supported. Nothing more, nothing less.

Prephrasing matters more than it might seem. If you predict your answer first, a trap choice has to beat your own prediction to tempt you. If you skip that step and read the choices cold, a well-written trap only has to sound plausible to pull you in.

The short version

• If you catch yourself reasoning from outside knowledge, common sense that isn't actually in the stimulus, stop. That's not what a must-be-true question rewards.
• Log which of the 3 reasoning structures trips you up: conditional chains, comparative numbers, or causal links. Most people are solid on 2 out of 3 and shaky on the third, that's the one to drill.
• On your next timed set, mark every must-be-true question where you predicted an answer before reading the choices. If your prephrase rate is under half, build that habit first, it does more for your accuracy than more content review.

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