Logical Reasoning · Sufficient Assumption

PrepTest 118 · Section 1 · Question 21

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

Step 1 · Pre-Question Guidance · read this first

Question type

Sufficient Assumption

The one idea it tests

If a link must show up every time, then finding cases where it fails is enough to deny the link.

The basic logic

The patty shows mismatches: A without B, and B without A. The top bun says no consistent link. The magic key: if there were a consistent link, it would always show up. Then mismatches click the conclusion shut.

Tiny words that decide it

“if...then”
“all”
“no consistent”
“many”

Playground logic

Tommy says the doorbell and Biscuit's barking aren't consistently linked, because Biscuit barks with no doorbell and the doorbell rings with no bark. The magic key is a rule: if they were consistently linked, every ring would bring a bark. Plug it in and the Click Test works.

Step 2 · The kid story

Biscuit and the Doorbell

Aunt Rosa claimed Biscuit barks because of the doorbell. Tommy wasn't so sure. Lulu kept a clipboard log for a week. Tuesday: doorbell rang, Biscuit snored. Wednesday: Biscuit barked at nothing, no doorbell anywhere. Friday: three rings, zero barks. Tommy announced, "So there's no steady link between the doorbell and the barking." Priya tilted her head. "Only if a steady link means it happens every single time. If a real link could skip now and then, your log doesn't prove much." Tommy thought. "Okay. If they were truly linked, every ring would get a bark. That's my rule." "Then your conclusion clicks," said Priya. Biscuit, hearing nothing, barked at the cat.

Step 3 · Try the model question

Some doorbell rings were not followed by barking. And some barking happened with no doorbell. So the doorbell and the barking are not consistently linked.

Which choice, if added, makes Tommy's conclusion follow for sure?

Step 4 · The courtroom tale

The Case of the Squeaky Gate

An invented neighbor sued, saying a squeaky gate always woke her baby. Mr. Whitfield showed a diary: nights the gate squeaked while the baby slept, and nights the baby woke with no squeak at all. "No steady link, Your Honor." The judge leaned in. "Counselor, does a steady link mean it must happen every time?" Mr. Whitfield nodded firmly. "If the squeak truly caused the waking, every squeak would wake her. One quiet sleep through a squeak breaks the chain." The judge wrote it down. "Granting that rule, your diary settles it."

Step 5 · Work the real question

Open PrepTest 118, Section 1, Question 21 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Spot the two kinds of mismatch in the patty and the 'no consistent link' top bun. A sufficient assumption must make the conclusion guaranteed. Look for a conditional that says a consistent link would show up every time, so one failure breaks it. Reject choices that only say many cases must line up, that reverse the conditional, or that say a link could survive gaps.