Logical Reasoning · Necessary Assumption

PrepTest 104 · 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

A prediction rides on a curve that gets better only as you move further along it, so the argument needs the mover to keep moving.

The basic logic

The patty: a problem peaks at a middle stage and shrinks as you go further. The subject is sitting at the peak. The top bun: the problem will shrink soon. The secret sauce: the subject will actually keep going further along the curve. Pull the Plank: if it stalls, the prediction collapses.

Tiny words that decide it

“because”
“then”
“should”

Playground logic

Owen is in the worst week of bike falls, so Marcus predicts his falls will drop soon. That only works if Owen keeps practicing. Pull that plank and Owen just stays stuck at the peak, falling forever.

Step 2 · The kid story

Owen and the Wobbly Week

Ms. Rivera's bike club keeps a fall chart. Beginners fall a little in week one, a lot in week three, and then hardly at all by week six, because practice builds balance. Owen just finished week three with eleven falls and two scraped elbows. Marcus announced, "Good news, Owen! You are at the top of the curve. The falls will drop any day now." Lulu flipped her clipboard. "Only if he keeps riding. The chart drops because kids keep practicing." Owen looked at his elbows. "I was thinking of switching to board games." Priya smiled. "Then the chart cannot help you. The curve only goes down for people who keep moving along it." Owen sighed, buckled his helmet, and wobbled off again.

Step 3 · Try the model question

Bike falls are worst around the third week of practice and drop after that, because more practice builds balance. Owen has just finished his third week. So Owen's falls should start dropping soon.

The argument relies on which assumption?

Step 4 · The courtroom tale

The Case of the Leaky Startup

A young bakery was sued for constantly late deliveries. Its lawyer, Mr. Whitfield, presented a chart. "New bakeries are late most often in their second year, when orders grow faster than staff. Then, as they keep growing, they earn enough to hire drivers and lateness falls. My client is in year two. Lateness will soon fall." The judge peered over her glasses. "Counselor, the chart says lateness falls as bakeries keep growing. Is your client going to keep growing?" Mr. Whitfield paused. "Well, the owner did mention closing the second oven." "Then your prediction has no floor under it," said the judge. Mr. Whitfield tugged his suspenders and asked for a short recess.

Step 5 · Work the real question

Open PrepTest 104, Section 1, Question 13 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Map the curve: what makes the problem rise, what makes it fall, and where the subject sits now. Notice why the problem falls: some ongoing change continues. Then ask what the subject must do for the prediction to come true. Use Pull the Plank on each choice: negate it and see whether the prediction crumbles. Skip choices that would help but are not required, or that talk about outsiders.