Logical Reasoning · Sufficient Assumption

PrepTest 145 · Section 2 · Question 9

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

Find the magic key that locks the premise to the conclusion so the conclusion simply has to follow.

The basic logic

The argument says a thing has feature X, and that being in the category requires feature Y. It never says X and Y can't live together. The key answer builds that bridge: anything with X lacks Y.

Tiny words that decide it

“must”
“no matter”
“cannot both”

Playground logic

Priya's argument has a patty (the fort can be rearranged by any visitor) and a rule (a Secret Fort needs a layout set by its builders), but the secret sauce is missing: nobody said a layout visitors can change isn't a layout set by the builders. Snap that piece in and the top bun clicks shut.

Step 2 · The kid story

The Fort That Wasn't Secret

At recess, Marcus announced that the pillow fort in the reading corner was an official Secret Fort. Priya sipped her juice box and shook her head. "Club rules," she said, tapping her notebook. "A Secret Fort has to have a layout set by the kids who built it. But this fort? Anyone who crawls in can move the pillows around. Kevin turned the tunnel into a dinosaur cave this morning." Marcus frowned. "So? Moving pillows doesn't mean the builders lost control." Lulu raised her clipboard. "That's the gap, Priya. You need one more rule: if visitors can change the layout, then the builders didn't set it." Priya grinned. "Exactly. Add that, and the fort is out of the club. No arguing." Biscuit flopped on a pillow, changing the layout yet again.

Step 3 · Try the model question

Priya: The reading-corner fort is not a Secret Fort. Any visitor who crawls in can rearrange its pillows. To count as a Secret Fort, a fort must have a layout set by the kids who built it.

Which one of the following, if assumed, makes Priya's conclusion follow?

Step 4 · The courtroom tale

The Case of the Choose-Your-Path Cake

Mr. Whitfield snapped his suspenders. "Your Honor, the bakery contest only accepts cakes whose design is fixed by the baker. My opponent's cake lets each guest pick the frosting color at the table." Judge Pemberton peered over her glasses. "And?" "And so it isn't eligible." The opposing lawyer jumped up. "Objection! Guests picking a color doesn't mean the baker gave up control of the design!" The judge nodded. "Mr. Whitfield, you need one more piece: a design guests can change is not a design fixed by the baker." Mr. Whitfield smiled. "Then I'll state it plainly, Your Honor. With that rule on the table, my conclusion follows automatically." The gavel came down. "Proven."

Step 5 · Work the real question

Open PrepTest 145, Section 2, Question 9 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Find the conclusion: something does not belong in a category. Find the feature the thing has and the feature the category requires. Ask what rule would make those two features clash. Look for the answer that says anything with the first feature cannot have the second. Run the Click Test: add it, and the conclusion must follow. Skip answers that leave the two features unconnected.