LSAT Must Be True and Most Strongly Supported Questions

Must Be True and Most Strongly Supported questions flip the usual LSAT task. Instead of judging an argument, you take the information as true and find what follows from it. These questions show up often, and the skill behind them (reading exactly what the text says, no more) carries into Reading Comprehension too. Here's the method I teach.

1How to spot them

Common stems:

• Must Be True: "If the statements above are true, which one of the following must also be true?"
• Most Strongly Supported: "The statements above, if true, most strongly support which one of the following?"
• Inference: "Which one of the following can be properly inferred from the information above?"

All three ask the same thing: which answer does the stimulus prove or nearly prove? The stimulus often has no conclusion at all, just a set of facts.

2The core rule: prove every word

The right answer is backed up by the text. Every part of it. Before you choose, point to the sentence or sentences that support each part of the answer. If one word has no support, the answer is wrong.

That makes these questions different from Strengthen or Assumption questions, where new information is welcome. Here, new information is the main way wrong answers are built.

3Must Be True vs. Most Strongly Supported

• Must Be True answers are 100% proven. There's no case where the stimulus is true and the answer is false.
• Most Strongly Supported answers are very likely given the stimulus, but may fall a little short of certain.

In practice, use the same method on both. Start by looking for an answer that must be true. Only if none qualifies do you settle for the most strongly supported one. You'll rarely need that fallback.

4The method

Step 1: Read for what's stated, not implied. Notice quantity words (all, most, some, none), certainty words (must, may, often) and conditionals (if, only if, unless).

Step 2: Look for combinations. The most-tested right answers combine two statements. If the stimulus says "most A are B" and "all B are C," then most A are C. Translate any conditionals and write their contrapositives. Our guide to "unless" and "only if" covers the translations.

Step 3: Make a loose prediction. You won't always predict the exact answer, but know what's provable: the end of a chain, a combined "some," a contrapositive.

Step 4: Eliminate by proof. For each answer, ask: where does the stimulus prove this? No evidence, no answer.

5Sample question (LSAT JET original)

At Linden Public Library, every book in the rare-books room was published before 1900. Most books published before 1900 that the library owns have never been digitized. Some books in the rare-books room are on loan from other libraries.

Which one of the following is most strongly supported by the information above?

(A) Most books in the rare-books room have never been digitized. (B) At least some books in the library that were published before 1900 are on loan from other libraries. (C) No book published after 1900 has been digitized. (D) Books on loan from other libraries are more likely to be digitized than books the library owns. (E) The rare-books room contains every book the library owns that was published before 1900.

Answer: (B).

• Some rare-books-room books are on loan. Every rare-books-room book was published before 1900. So those loaned books were published before 1900. That proves (B).
• (A) is the tempting one. But the "most" statement is only about pre-1900 books the library owns, and we don't know how much of the rare-books room is owned versus borrowed, or whether its pre-1900 books are typical. "Most" doesn't carry over to a subset. Not proven.
• (C) is new information about post-1900 books. Nothing supports it.
• (D) compares digitizing rates the stimulus never mentions.
• (E) reverses the first statement. Rare-books room → pre-1900 doesn't mean pre-1900 → rare-books room.

6The four traps

1. Too strong. The stimulus says "some" or "often," and the answer says "most" or "always." Watch for "most" claims carried over to a smaller group, as in (A) above.
2. New information. The answer brings in a comparison, a cause or a topic the stimulus never discussed.
3. Could be true. The answer is consistent with the stimulus but not proven by it. "Could be true" is not "must be true."
4. Reversed conditional. The answer flips an if-then. "All A are B" doesn't mean "all B are A."

Strong language isn't always wrong here. If the stimulus says "all," an answer that says "all" can be proven. The test is whether the text supports the strength, not whether the word sounds extreme.

7Quantity words: the combinations that work

A short list worth knowing, because the LSAT tests it often:

The last two rows are where trap answers come from. Two "some" or two "most" statements that share a middle term don't connect.

8How to practice

• On your next ten Must Be True or Most Strongly Supported questions, write the line number or sentence that proves your answer before you check the key.
• For every wrong answer you eliminate, label it with one of the four traps.
• After a diagnostic or practice test, count how often each trap caught you. The biggest number is your next drill.