Logical Reasoning · Necessary Assumption

PrepTest 124 · Section 1 · Question 13

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

Step 1 · Pre-Question Guidance · read this first

Question type

Necessary Assumption

The one idea it tests

When a short absence of a supposed cause shows no change, concluding the cause does nothing assumes that the absence would have revealed an effect if one existed.

The basic logic

The patty: during a pause in X, Y stayed the same. The top bun: X has no effect on Y. The secret sauce: if X mattered, the pause was enough to show a change. Pull the Plank: if the pause was too short to matter, the argument fails.

Tiny words that decide it

“no significant change”
“thus”
“no effect”

Playground logic

Marcus says the hallway quiet sign does nothing because the hall stayed just as noisy the week it was down. His secret sauce is that a working sign, once removed, would have made a difference within that week.

Step 2 · The kid story

The Quiet Sign Mystery

Last fall, Ms. Rivera hung a giant QUIET PLEASE sign in the hallway. Some kids say the hall has been calmer ever since. But last week, the sign came down for repainting. Marcus had his detective notebook ready. "I measured the noise all week with my phone app. No change at all! So the sign does nothing." Priya frowned over her juice box. "Hmm. That only works if taking the sign away for one week would have made the hall louder, if the sign really worked." Lulu looked up from her clipboard. "Maybe kids remember the sign even when it's gone, like how Biscuit still sits by the treat jar after it's empty." Marcus grumbled. "Fine. I'm assuming the sign's effect would show up fast."

Step 3 · Try the model question

Some kids credit the new hallway sign for making the hall quieter since it went up. But during a week when the sign was taken down for repainting, the hallway noise did not change. So the sign has no effect on hallway noise.

Which unstated belief does the sign argument lean on?

Step 4 · The courtroom tale

The Case of the Silent Scarecrow

A farmer sued the scarecrow maker, claiming the scarecrow did nothing. "I took it down for two days during a storm," he testified, "and the crows didn't come back. So the scarecrow never mattered." Mr. Whitfield smoothed his suspenders. "Sir, do crows return to a field the moment a scarecrow vanishes?" "Well, maybe not that fast." "So two days might be far too short to see any difference." Whitfield turned to the jury. "The farmer's case assumes that a working scarecrow, once gone, would bring crows back within two days. Without that, his quiet field proves nothing."

Step 5 · Work the real question

Open PrepTest 124, Section 1, Question 13 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Identify the test window: a short period when the supposed cause was absent. Note that the effect stayed steady during it. The conclusion denies any effect at all. Look for the answer that says a real effect would have shown up during that window. Check by negating: if the window could hide a real effect, the argument loses its evidence.