Logical Reasoning · Flaw
PrepTest 138 · Section 2 · Question 7
Phase 1 (your first ~400 questions): read the guidance, then answer. No clock.
Step 1 · Pre-Question Guidance · read this first
- “no”
- “thus”
- “false”
Playground logic
Grandpa says rubbing his lucky button helps him win at checkers. Marcus notes that nobody has ever proven it works, then declares Grandpa's claim false. The patty is 'no proof', the top bun is 'false', and the secret sauce is the No Footprints mistake: no footprints does not mean nobody walked there.
Step 2 · The kid story
Grandpa's Lucky Button
Grandpa has a shiny brass button he rubs before every checkers game. 'This button helps me win,' he says. Grandpa wins a lot. Marcus put on his detective hat. 'Has anyone ever done a real test? Like, a hundred games with the button and a hundred without?' Grandpa admitted nobody had. 'Aha!' said Marcus. 'No one has proven the button works. So Grandpa's claim is false!' Lulu frowned at her clipboard. 'Wait. Nobody proved it works. But nobody proved it does not work either.' Priya nodded. 'Marcus found no footprints and decided nobody was ever in the room. Maybe the button does nothing. Maybe it calms Grandpa down. We just do not know yet.' Grandpa winked and jumped three of Marcus's pieces.
Step 3 · Try the model question
Grandpa claims that rubbing his lucky button helps him win at checkers. Because of this, Tommy now rubs a button before his games too. But no careful test has ever shown that rubbing a button helps anyone win at checkers. So Grandpa's claim is false.
Which choice names a mistake in the reasoning above?
Step 4 · The courtroom tale
The Case of the Singing Tomatoes
A gardener's shop sign said: Our music box helps tomatoes grow. A rival shop sued, calling the sign a lie. Their lawyer said, 'Your Honor, there is no scientific study showing music helps tomatoes. Therefore the sign is false.' Mr. Whitfield tugged his suspenders. 'Counsel has shown that nobody has tested it. He has not shown the sign is wrong. No study either way means we do not know. An empty room is not proof that nobody ever lived there.' Judge Harlow tapped her pen. 'The plaintiff must show the claim is false, not merely unproven. Try again with evidence.'
Step 5 · Work the real question
Open PrepTest 138, Section 2, Question 7 in your official copy from LSAC (for example in LawHub) and read it there.
Your answer
How to apply it
Find the conclusion and look at its strength: does it call some claim untrue? Then find the evidence. If the evidence is only that nothing has proven the claim, you have No Footprints. Predict a description like 'treats lack of proof as disproof'. Match that idea in abstract wording. Skip Phantom Pieces that name a flaw the argument never commits, however familiar they sound.