Logical Reasoning · Sufficient Assumption

PrepTest 151 · Section 3 · Question 12

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 missing link that, once added, makes the conclusion follow with certainty.

The basic logic

The argument has a rule: the item counts as proof only if a condition holds. Then it gives a fact that sounds related to the condition but uses a different word. The conclusion says the condition fails. The gap is the bridge between the fact's word and the condition's word. The right answer builds exactly that bridge so the Click Test works.

Tiny words that decide it

“only if”
“if”
“so”

Playground logic

The rule: Tommy's sandcastle counts for the solo prize only if one builder made it. The patty: it's a patchwork of chunks built at different spots on the beach. Top bun: so it doesn't count. The magic key: if it's a patchwork from different spots, then more than one builder made it. Add that key and the argument clicks.

Step 2 · The kid story

The Patchwork Sandcastle

At the beach contest, the sign read: 'Solo Prize: castle must be built by ONE builder.' Tommy proudly pointed at his tall castle. Marcus squinted. "This castle was put together from chunks built at different spots on the beach. The towers came from the north end. The wall came from by the lifeguard stand. So it doesn't count for the solo prize." Tommy crossed his arms. "Says who? Maybe I built every chunk myself and just carried them over!" Priya sipped her juice box. "Marcus, your argument needs one more piece. You have to show that chunks from different spots mean more than one builder. Then it clicks." Marcus sighed. "Fine. Lulu, who built the wall?" Lulu checked her clipboard. "Kevin."

Step 3 · Try the model question

Tommy's castle can win the solo prize only if a single builder made the whole castle. But the castle is a patchwork of chunks built at different spots on the beach. So it cannot win the solo prize.

Adding which statement would guarantee the conclusion?

Step 4 · The courtroom tale

The Quilt Contest

Judge Okafor read the county fair rules aloud. "The heirloom ribbon goes to a quilt only if the entire quilt was sewn by one person." The fair's lawyer pointed to Exhibit A. "Your Honor, this quilt is made of squares stitched in five different towns. So it cannot win the heirloom ribbon." Mr. Whitfield stood, adjusting his suspenders. "Your Honor, my client traveled to all five towns. Squares from five towns do not prove five sewers." The judge turned to the fair's lawyer. "Counselor, your conclusion only follows if squares from many towns means many sewers. Can you show that?" The lawyer shuffled papers. Mr. Whitfield smiled. "Without that link, Your Honor, the argument doesn't click."

Step 5 · Work the real question

Open PrepTest 151, Section 3, Question 12 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Write out the conditional rule in the argument and note exactly which term it uses. Then note the term used in the fact that follows. If the two terms differ, predict an answer that links the fact's term to the failure of the rule's condition, in the right direction. Test each choice by adding it to the argument: if the conclusion now follows with certainty, it is your answer. Discard choices that only make the conclusion more likely or add new topics.