Logical Reasoning · Sufficient Assumption

PrepTest 119 · Section 4 · Question 21

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

When the conclusion uses a term the premises never mention, the magic key must connect the premise's feature directly to that new term.

The basic logic

The premises say one group is the only one with a certain feature, and that the feature makes something easy. The conclusion says this group does a different thing better than everyone else. Find the bridge: anyone with the feature always does the new thing better than those without it.

Tiny words that decide it

“only”
“always”
“better than”

Playground logic

Owen is the only dog walker who keeps a notebook of every dog's habits, and the notebook makes it easy to spot who needs extra walks. Then he concludes his dogs come home happier than anyone else's. The secret sauce: any walker who keeps such a notebook always brings dogs home happier than walkers who do not.

Step 2 · The kid story

Owen's Notebook of Dogs

Owen started a dog-walking club with his notebook. "I am the only walker on our street who writes down every dog's walk times and favorite squeaky toy," he told Nadia. "Just by sorting my notes, I can see which dogs need long walks and which need short ones." "Cool," said Nadia. "So my dogs come home happier than anybody else's dogs," Owen finished. Priya looked up from her juice box. "Whoa. Your evidence is about notes and sorting. Your ending is about happy dogs. Where is the bridge?" Lulu tapped her clipboard. "You need a rule like: walkers who keep notes like that always bring dogs home happier than walkers who do not." Biscuit wagged his tail in agreement, or possibly because he smelled a treat.

Step 3 · Try the model question

Owen: I am the only dog walker on our street who records every dog's walk times and favorite toy. Simply by sorting these notes, I can easily tell which dogs need long walks. So the dogs I walk come home happier than the dogs other walkers take out.

Which assumption would make Owen's conclusion follow for sure?

Step 4 · The courtroom tale

The Case of the Tidy Tailor

Two tailors fought over a 'Best Fit in Town' sign. Ms. Lee, for the first tailor, argued, "Your Honor, my client is the only tailor who measures every customer twelve times. With those numbers, she easily sees every lump and bump. Therefore her suits fit better than any other tailor's suits." Mr. Whitfield objected. "Measuring is not fitting. Where is the link?" Ms. Lee smiled. "Here: any tailor who measures that carefully always produces better fits than tailors who do not." The judge nodded. "Accept that, and the sign is hers. Without it, all we know is she owns a very tired tape measure."

Step 5 · Work the real question

Open PrepTest 119, Section 4, Question 21 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Write the conclusion and circle the term that appears only there. Then write the feature the premises give the group. The right answer must take that exact feature and guarantee the conclusion's new term, and it must be strong enough (always, any) to produce a 'better than everyone else' result. Plug each choice in. If the conclusion still might be false, the key does not click. Watch out for choices that are only needed, not enough.