LSAT Must Be False Question Tips

A must be false question asks which answer choice cannot be true if the facts in the stimulus are true. The method is backwards from almost every other question type: do not hunt for the answer that is proven. Test each choice by asking whether it could be true, eliminate every choice that could be, and keep the one that is impossible given the facts.

How do you answer an LSAT must be false question?

Read the stem first, so you know you are hunting for falsity before you read the facts. Then read the stimulus as a set of rules, not as an argument to agree or disagree with. Most must be false stimuli are not arguments at all. They are a list of facts, conditions, or rules, and your job is to find the one answer choice that breaks one of them. For each choice, ask one question: "Can this happen while every stated fact stays true?" If yes, or even maybe, eliminate it. If no, because it directly contradicts a fact or a valid deduction from the facts, that is your answer.

How to spot a must be false question

The stem gives the type away, but the wording varies. Watch for these forms:

• "If the statements above are true, which one of the following must be false?"
• "Which one of the following cannot be true?"
• "Which one of the following is inconsistent with the information above?"
• "Which one of the following, if true, would violate the rules above?" or "...contradicts the statements above?"

Two lookalikes deserve a warning. "Which one of the following could be false?" is a different, much easier question: there, any choice that is not proven counts, and four choices can qualify. "Which one of the following is not necessarily true?" is also different: it asks for something unproven, not something impossible. Must be false is the strictest of the family. The answer must be impossible, not merely unproven.

The could-be-true test: the one method that decides these questions

Here is the method, stated precisely. For each answer choice:

1. Imagine a scenario in which the choice is true.
2. Check that scenario against every stated fact. Does it break any of them?
3. If you can build even one scenario where the choice holds and no fact breaks, eliminate the choice. It could be true.
4. Keep the choice only if every scenario you try breaks at least one fact.

That "even one scenario" standard is the whole game. Students lose these questions by applying the wrong standard: they eliminate choices that seem unlikely, or keep a choice because the facts never mention it. Likelihood is irrelevant. Silence is irrelevant. Only impossibility counts. If a choice describes something the facts never address, it could be true, so it gets eliminated.

Must be false questions are the mirror image of must be true questions. In a must be true question, you keep the choice that is proven and eliminate everything else. Here, you eliminate everything that is possible and keep the choice that is disproven. Our inference question guide covers the must-be-true side of the family, and the same fact-reading discipline applies to both.

A worked example

Consider this original set of facts, written in LSAT style:

"A community center offers exactly four evening classes: pottery, coding, yoga, and Spanish. Each class meets once a week. Pottery meets on Monday. Coding meets the day after pottery. Yoga does not meet on Monday or Tuesday. Spanish meets on a day after yoga."

From these facts, you can pin down part of the schedule. Pottery is Monday, so coding is Tuesday. Yoga cannot be Monday or Tuesday, and Spanish must come after yoga, so the earliest yoga can meet is Wednesday and the earliest Spanish can meet is Thursday. Now consider two candidate answers to "which one of the following must be false?":

• "Yoga meets on Wednesday." This could be true. Wednesday is one of the days yoga could meet. Eliminate it. A choice being possible is enough to rule it out here.
• "Spanish meets on Tuesday." This cannot be true. Coding is Tuesday, Spanish must come after yoga, and yoga cannot be Monday or Tuesday, so Spanish cannot be earlier than Thursday. This breaks the rules, so this is the shape of a correct answer.

Notice what the example teaches. You did not need to prove the correct answer from scratch. You needed to test each choice against the rules until one broke. On the real test, the rules are usually less tidy than this example, a mix of conditionals, comparisons, and quantities, but the test is identical: can this choice coexist with every fact?

The 4-step routine

1. Read the stem first. Knowing you need falsity changes how you read. You are collecting rules to test choices against, not looking for a conclusion to support or attack.
2. Map the facts. Note the hard constraints: numbers, dates, orderings, conditionals, and exclusions. A short sketch, even a few symbols, beats re-reading the stimulus five times. Pay special attention to words like "exactly," "only," "never," and "at least," because those words are what make an answer impossible rather than merely unlikely.
3. Eliminate the could-be-trues. Go through the choices and cross out anything you can imagine being true. Do the easy eliminations first. Usually two or three choices fall immediately, because they restate a fact or describe something plainly allowed.
4. Verify the survivor. Before you commit, point to the fact it breaks. If you cannot name the broken fact, you have not found the answer yet. You have found a choice that merely feels wrong, which is how the unproven-but-possible trap wins.

On timing, budget more than the usual 80 to 90 seconds for these. Must be false questions are slow because they ask you to test five choices against a rule set instead of matching one answer to a conclusion. Tutors often describe them as appearing only about once or twice per test, so the extra time is affordable. If one stalls you past about two minutes, mark your best guess, flag it, and move on. The full type list lives in our Logical Reasoning question types guide.

Must be false vs. its lookalikes

The "except" variant is worth flagging because it hides the type. A stem like "Each of the following could be true EXCEPT" is a must be false question wearing different clothes. Four choices will be possible, and one will be impossible. Run the same could-be-true test.

Traps that catch good students

• The unproven answer. A choice the facts never mention feels wrong, but silence is not contradiction. If it could happen, eliminate it.
• The unlikely answer. A choice describing a weird or rare scenario is still possible. Must be false demands impossibility, not improbability.
• The real-world false answer. A choice that is false in real life can still be true under the stimulus. Only the given facts count, never outside knowledge.
• The half-contradiction. A choice that conflicts with one reading of a fact but fits another. Check the exact wording, especially quantifiers. "Some" leaves room that "all" does not.
• The opposite answer. A choice that must be true is tempting because it feels certain. Certainty in the wrong direction is still the wrong answer. Certainty that something is true is the opposite of what this question asks.

How to practice must be false questions

Because the type is rare, do not drill it in isolation for hours. Instead, fold it into your normal Logical Reasoning practice:

1. When you review any inference question, ask the mirror question: "What would have to be false here?" That turns every must-be-true question into must-be-false practice.
2. For each miss, write the broken fact in one sentence in your miss log: which fact the right answer contradicted, and which standard you applied instead. That sentence is what stops the next unproven-answer trap.
3. Practice rule-set stimuli specifically, since most must be false questions use them. Scheduling rules, grouping rules, and conditional chains are the usual shapes. Once the could-be-true test feels automatic, stop drilling the type and spend your time on flaw, strengthen, and assumption questions, which appear far more often.

As of October 2026, the current LSAT format has two scored Logical Reasoning sections, so a rare must be false question can appear in either one. The method does not change between sections. Read the stem first, map the facts, eliminate everything that could be true, and verify the survivor against a named fact.