Logical Reasoning · Necessary Assumption

PrepTest 150 · Section 2 · Question 2

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 picture of something proves when a place was in use only if the picture was made while the place was in use.

The basic logic

The patty: something existed only before a certain time, and a picture of it was found at a site. The top bun: the site was in use before that time. The gap is about timing. Use the Pull the Plank test: if the picture was made at some other time, does the argument fall?

Tiny words that decide it

“until”
“shows”
“at a time when”

Playground logic

Nadia finds a chalk drawing of the old ice cream truck in the clubhouse and says the club met back when the truck still came. The secret sauce is that the drawing was made by someone using the clubhouse back then. Pull that plank and the argument sinks.

Step 2 · The kid story

The Chalk Truck Mystery

The Purple Ice Cream Truck used to visit Maple Lane every afternoon, until it stopped coming three summers ago. Yesterday Nadia cleaned the old clubhouse behind Owen's garage and found a chalk drawing of the Purple Truck on the wall, sprinkles and all. "Aha!" said Nadia. "This proves kids used this clubhouse back when the truck still came." Owen scratched his head. "Unless my cousin drew it last week. He loved that truck. He draws it everywhere." Lulu raised her clipboard. "So the drawing only helps if somebody made it during the clubhouse days." Nadia sighed. "Fine. My whole case leans on when the chalk went up." Biscuit sniffed the wall and sneezed chalk dust.

Step 3 · Try the model question

The Purple Truck stopped visiting Maple Lane three summers ago. A chalk drawing of the Purple Truck was found inside the clubhouse. So kids were using the clubhouse while the truck was still visiting.

Nadia's conclusion depends on which assumption?

Step 4 · The courtroom tale

The Painted Trolley

The town's old trolley stopped running fifty years ago. A lawyer for the Historical Club held up a painted tile. "Your Honor, this tile shows the trolley, and we found it in the old bakery. So the bakery was open back when the trolley ran!" Mr. Whitfield rose slowly. "Counselor, when was the tile painted?" "It shows the trolley." "Lots of things show the trolley. My nephew painted one on a mug last spring." The judge nodded. "Your argument needs the tile to be made while the bakery was open. Prove that piece, or the timeline falls apart."

Step 5 · Work the real question

Open PrepTest 150, Section 2, Question 2 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Find the time limit in the premises and the time claim in the conclusion. Notice that the evidence is an object that shows something, not a date. Ask what has to be true for that object to tell you about the time the place was in use. Test each choice with Pull the Plank: negate it and see whether the conclusion collapses. The right answer ties the making of the object to the period in question.