LSAT Necessary Assumption Practice Question: Argument by Analogy
An original necessary assumption question from our free Question of the Day rotation, built around a trap the LSAT reuses constantly: argument by analogy. Try it first, then read the explanation — it teaches the move, not just the answer.
Your job:Find what the argument must be assuming.
Ferndale launched a monthly night market two years ago, and it now draws thousands of visitors. Bridgeton's town council has approved a night market of its own, reasoning that because Ferndale's market succeeded, Bridgeton's will succeed as well.
Which one of the following is an assumption the council's argument requires?
Show the answer & full explanation
The correct answer is B
The JBDM line
Just because it worked in Ferndale doesn't mean it will work in Bridgeton.
The maybes
- MaybeMaybe Ferndale sits on a tourist highway and Bridgeton doesn't.
- MaybeMaybe Ferndale's success came from a famous food scene Bridgeton lacks.
Why B is right
Negate it: suppose Ferndale's success DID come from something Bridgeton lacks — a tourist corridor, a famous vendor, a bigger population. The analogy dies instantly, and so does the conclusion. Every argument by analogy quietly assumes the differences don't matter; this answer states that assumption.
Why the others are wrong
- AShared visitors aren't required — Bridgeton's market could succeed with an entirely different crowd.
- C'Every town' is wildly stronger than the argument needs; that's sufficient-assumption energy, not necessary.
- DSuccess doesn't require the same vendors, just conditions that work.
- EWhat Ferndale's council once thought is trivia, not a load-bearing assumption.
Sammy's note
Arguments by analogy assume the differences don't matter. That hidden assumption is usually the answer.
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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