Logical Reasoning · Necessary Assumption

PrepTest 144 · Section 3 · 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

If you say option one is worse than option two because of a defect, you must assume option two lacks that defect.

The basic logic

The argument blames one option for a defect that drives people away, and concludes the rival option would do better. The gap: nothing says the rival is free of the same defect. Pull the plank: if the rival had the defect too, the comparison falls.

Tiny words that decide it

“thus”
“as effectively as”
“unlikely”

Playground logic

Marcus says Nadia's version of the recess game rules will keep more players than Kevin's, because Kevin made the game sound like something it isn't. The secret sauce: Nadia's version didn't twist the game too.

Step 2 · The kid story

Two Ways to Explain Capture the Flag

Kevin explains capture the flag to the new kids. "It's a dinosaur game! You get to be a T. rex and roar!" The new kids show up expecting dinosaurs, find out it's just running with flags, and quit after one round. Marcus shakes his head. "Kevin's explanation was totally wrong. Nadia's explanation would have kept way more players coming back, because kids who show up expecting the wrong thing leave." Lulu raises her pencil. "Hold on. That only works if Nadia's explanation was accurate. What if she said it was a pirate treasure hunt?" Priya nods. "Pull that plank and the argument sinks. If Nadia also twisted the game, her version would lose players just like Kevin's."

Step 3 · Try the model question

Kevin's explanation of the recess game badly misdescribed it. So it will not keep as many players coming back as Nadia's explanation would have, since kids who join expecting the wrong game tend to quit.

Marcus's argument requires which one of the following to be assumed?

Step 4 · The courtroom tale

The Two Tour Guides

A museum sued a tour company, claiming its guide's speech drove visitors away. The museum's lawyer argued, "The guide described the exhibit as a thrilling ride. Visitors expecting a ride left disappointed. Our own guide's speech would have kept them." Mr. Whitfield rose, suspenders gleaming. "Your Honor, that holds only if the museum's own speech was honest. If their guide also promised a roller coaster, visitors would have left just the same." The judge turned to the museum's lawyer. "Can you show your speech was accurate?" The lawyer shuffled papers. "We assumed so, Your Honor." "Then your case rests on an assumption you need to prove."

Step 5 · Work the real question

Open PrepTest 144, Section 3, Question 13 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Find the conclusion: one option will do worse than a rival option. Find the reason: the first option has a defect that makes people leave. Ask what must also be true about the rival for the comparison to work. Pull the plank on each choice: negate it and see if the argument breaks. Reject choices that are stronger than needed or about something besides the two options.