LSAT Inference Practice Question: Must Be True
An original inference question from our free Question of the Day rotation, built around a trap the LSAT reuses constantly: must be true. Try it first, then read the explanation — it teaches the move, not just the answer.
Your job:Find what the statements force to be true.
In the Tamsen Nature Reserve, no trail that crosses the wetland is open to visitors during spring nesting season. The Heron Loop trail crosses the wetland. Several of the reserve's trails that are open during nesting season are steep, and steep trails require permits year-round.
If the statements above are true, which one of the following must be true?
Show the answer & full explanation
The correct answer is B
The JBDM line
Just because several open trails are steep doesn't mean most are — and just because a rule closes a trail doesn't tell you anything else about it.
The maybes
- MaybeMaybe the Heron Loop is pancake-flat — nothing says otherwise.
- MaybeMaybe only three of forty open trails are steep, so 'most' fails.
Why B is right
Apply the rule: no wetland-crossing trail is open during nesting season, and the Heron Loop crosses the wetland. Closed during nesting season — forced, no escape hatch. Everything else in the stimulus is scenery designed to tempt you past the one airtight chain.
Why the others are wrong
- ANothing links the Heron Loop to steepness; it could be flat.
- CPermits attach to steep trails, and we don't know the Heron Loop is steep.
- D'Several' steep trails could be a small minority of the open ones — 'most' overreaches.
- EThe rule says wetland trails are closed; it never promises non-wetland trails are open.
Sammy's note
Must-be-true means forced. If you can imagine one world where it's false, it's out.
What's a JBDM line?
Just Because Doesn't Mean (JBDM) is the Burton Method's foundational framework for attacking LSAT arguments: identify the premise, identify the conclusion, then say "just because [premise] doesn't mean [conclusion]" and generate "maybes" — alternative explanations that expose the gap between them. That gap is what weaken, flaw, strengthen, and assumption questions all test, so every explanation on this page starts with the JBDM line. It's a micro-lesson in the system, not just an answer key.
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Answer today's question and start a streak — then see how Sammy teaches the whole system, JBDM included, in a free lesson.