Inference Questions
The facts are given. Your job is to say what they force.
Two tools pair with this method. The miss-pattern analyzer shows which question types cost you the most points, and the blind review worksheet gives you a second pass at every miss.
What the question asks
The question asks what must be true given the statements. The stem says something like "Which one of the following can be properly inferred?" or "If the statements above are true, which one of the following must be true?"
The right answer follows from the facts alone. It adds no new claims and needs no outside knowledge. If a choice needs even one extra fact, it is wrong.
Step-by-step method
- Take the statements at face value. Do not question them and do not add to them. Your only material is what is on the page.
- Combine them. Chain conditionals together. Link categories. Two facts that share a term often produce a third fact.
- Stay conservative. "Some," "not all," and negatives are safer than "all" and "most." The right answer is usually the modest one.
- Watch for the contrapositive. "If P then Q" plus "not Q" gives "not P." This single move answers a large share of inference questions.
- Reject anything extra. If a choice could be true but does not have to be true, it is wrong. "Must be true" is a strict standard.
Worked examples
Both examples are original. They are not real LSAT questions.
Example 1
Whenever the alarm sounds, the front doors lock. This morning the front doors did not lock.
Which one of the following must be true?
The answer: The alarm did not sound this morning.
Why: If alarm, then lock. No lock means no alarm. That is the contrapositive, and it must be true. Note the reverse would be wrong: locked doors would not prove the alarm sounded.
Example 2
All of the red marbles are inside the box. Some marbles inside the box are cracked.
If the statements above are true, which one of the following must be true?
The answer: No red marble is outside the box.
Why: That is a restatement of the first fact, so it must be true. And note what you cannot infer: you cannot say a red marble is cracked. The cracked marbles might all be blue.
Inference answers are boring on purpose
The right answer on an inference question is almost always the least exciting choice on the page. It restates what the facts already contain, in slightly different words. Students miss these questions because they go hunting for insight. There is no insight to find. Must be true means must, not might.
The discipline is in the strength of the words. If the premises say "some," the answer cannot say "most." If the premises describe one city, the answer cannot claim a national trend. Read each choice as a contract: is every word in this choice paid for by the facts? The moment a choice spends a word the facts did not earn, it is wrong.
Combination is the one creative move the type allows. The answer may put premise one and premise two together in a way the stimulus never states outright. That is still deduction, not invention. Check the combination against each premise separately. If both premises support it, it stands. If it needs anything the premises do not say, it falls.
Common traps
- A choice that could be true but does not have to be. Possibility is not inference.
- A choice that goes one step beyond the facts. One extra step is one too many.
- A choice that contradicts a statement. Check each choice against every given fact.
- A choice that confuses "some" with "most." The statements rarely support the stronger word.
Practice the method
The free diagnostic scores every LR question type and shows exactly where you are losing points.