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Logical Reasoning · Parallel Flaw

PrepTest 154 · Section 2 · Question 10

Phase 1 (your first ~400 questions): read the guidance, then answer. No clock.

Step 1 · Pre-Question Guidance · read this first

Question type
Parallel Flaw
The one idea it tests
A claim about most cases cannot be knocked down by one or two cases that go the other way.
The basic logic
The argument quotes a source saying most things of a kind will turn out a certain way unless something is done. Then it points to the arguer's own few cases where that thing was not done and nothing bad happened, and calls the source wrong. Match the answer with the same shape: a 'most... unless' claim, a tiny personal counterexample, a 'so it's false' ending.
Tiny words that decide it
  • “most”
  • “unless”
  • “false”
  • “never”

Playground logic

Kevin's coach says most kids who skip stretching will pull a muscle. Kevin never stretches, and he has never pulled anything, so he calls the coach wrong (top bun). His patty is just one kid, and a 'most' claim leaves room for lucky exceptions. That is a Tiny Sample plus a Scope Shift from 'most' to 'every'.

Step 2 · The kid story

Kevin Never Stretches

Coach Bell blew her whistle. "Most kids who skip stretching before soccer will pull a muscle this season." Kevin raised his hand. "Coach, that's wrong. I never stretch. I've played soccer for three seasons. I have never pulled anything. Not even a little." Lulu looked up from her clipboard. "Kevin, she said most kids. Not all kids." "But I am a kid!" said Kevin. "And I am fine. Also, did you know a T. rex couldn't touch its toes either?" Lulu wrote something down. "One kid who got lucky doesn't show the coach is wrong about most kids. If ninety out of a hundred non-stretchers get hurt, you could just be one of the other ten." Kevin thought about it. Then he quietly did a toe touch.

Step 3 · Try the model question

Coach Bell says that most kids who do not stretch before soccer will pull a muscle at some point. But the coach is mistaken. Kevin has never stretched before a game in three seasons, and he has never pulled a muscle.

Which one of the following shows a flawed pattern of reasoning most like the one above?

Choices

Step 4 · The courtroom tale

The Case of the Unwatered Ferns

Lawyer Crane addressed the court. "The garden expert testified that most ferns die within a month unless watered weekly. Rubbish! My client has two ferns. She has not watered them since spring. They are thriving." Mr. Whitfield stood up. "Your Honor, did the expert say every fern?" "No," said the judge, checking her notes. "She said most." "Then two happy ferns prove nothing," said Mr. Whitfield. "Maybe they sit by a leaky gutter. Maybe they are simply lucky. A 'most' claim expects a few survivors." The judge nodded. "Two ferns cannot outvote the rest of the forest."

Step 5 · Work the real question

Open PrepTest 154, Section 2, Question 10 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Write the original's skeleton in plain terms: who claims what about most cases, what condition, what tiny counterexample, what ending. Then x-ray each answer. Check the quantifier (most versus always), check that the counterexample skips the step and avoids the bad result, and check the ending rejects the claim. Cross out answers that attack the speaker, flip the direction, or predict instead of reject.