Logical Reasoning · Flaw

PrepTest 116 · Section 2 · Question 25

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

Step 1 · Pre-Question Guidance · read this first

Question type

Flaw

The one idea it tests

A requirement for success is not the only possible cause of failure.

The basic logic

The premise says something catches on only if a condition is met. The argument sees an early failure and concludes the condition was missing then. But a missing requirement is just one way to fail. Many other things could explain it.

Tiny words that decide it

“only when”
“must have”
“hence”

Playground logic

Ms. Rivera's class says a game catches on only when it matches what the class likes, and since a board game flopped in September but caught on in March, the class's tastes must have changed. That's a Flipped Switch: failure doesn't prove the requirement was missing, since maybe the first copy was missing pieces.

Step 2 · The kid story

The Planet Hop Puzzle

In September, Ms. Rivera brought in a board game called Planet Hop. Everyone played for two days, then the box sat on a shelf until March, when suddenly the whole class was hooked. Marcus put on his detective hat. "A game only catches on when it fits what the class cares about. So the class's interests must have changed between September and March!" Priya raised her juice box. "Or the September copy was missing half its pieces. I remember the spinner was broken." Nadia added, "And in March it was too rainy for recess." Lulu wrote: fitting the class is needed, not the only thing needed. Something else could have sunk the game in September. Marcus ignored every other explanation.

Step 3 · Try the model question

Planet Hop was played briefly in September, then ignored until March, when the class embraced it. A game catches on only when it fits the class's interests. So the class's interests must have changed between September and March.

The reasoning goes wrong because it

Step 4 · The courtroom tale

The Failed Food Truck

A city lawyer argued: "A food truck succeeds only if it serves food the neighborhood likes. The taco truck failed on Elm Street last spring but thrived there this fall. So the neighborhood's taste must have changed." Mr. Whitfield stood up. "Your Honor, last spring the street was torn up for construction. Nobody could park. Also, the truck's grill was broken for a month." The judge raised an eyebrow. "Counselor, liking the food is required for success, but it is not the only way to fail. You skipped right past the other explanations."

Step 5 · Work the real question

Open PrepTest 116, Section 2, Question 25 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Find the conditional premise: success requires a certain condition. Find the observation: an early failure followed by later success. Notice the conclusion blames the failure on the missing condition. Ask: could something else explain the failure? Predict the flaw: it ignores other explanations. Choose the answer naming that gap, and skip choices about side details the argument never uses.