Logical Reasoning · Necessary Assumption

PrepTest 116 · Section 2 · Question 23

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

When evidence ends at X and the conclusion is about Y, the argument needs X to matter for Y.

The basic logic

Trace the chain of premises to its last link. Then look at the conclusion. The term in the conclusion that never appeared in the premises must be connected to the last link. That bridge is the assumption.

Tiny words that decide it

“leads to”
“clearly, then”
“in addition”

Playground logic

Tommy's evidence ends at 'he can't make his own lunch anymore,' but his top bun says Grandpa's lunches make him worse off overall. The secret sauce: being able to do things yourself is part of being well off.

Step 2 · The kid story

Grandpa's Lunch Service

Every morning, Grandpa packed Tommy's lunch: a sandwich cut into stars, a pickle, and a cookie with a note. Tommy loved it. But Lulu, clipboard in hand, made a speech at dinner. "Grandpa's lunches save Tommy from all the work of making food. So Tommy now depends on Grandpa, and on Grandpa's grocery trips. That means Tommy can't take care of himself at lunch anymore. So besides making lunch less of an adventure, Grandpa's lunches make Tommy worse off overall." Priya, visiting, raised her juice box. "Your speech jumps. You showed he can't do it himself. You never showed that doing it yourself is part of being well off." Lulu added a line to her clipboard: being self-reliant helps a person be well off. Without that plank, the whole speech sinks.

Step 3 · Try the model question

Grandpa's lunches spare Tommy the work of making food, so Tommy depends on Grandpa and on Grandpa's grocery trips. This leaves Tommy unable to take care of himself at lunch. So, besides making lunch less of an adventure, Grandpa's lunches make Tommy worse off overall.

The argument depends on which assumption?

Step 4 · The courtroom tale

The Valet Lawsuit

A hotel guest sued, claiming the valet service harmed him. His lawyer argued: "The valet parks his car every day, so he relies on the valet staff. He has forgotten how to parallel park. Therefore, besides spoiling the joy of driving, the valet service has made him worse off." Mr. Whitfield, for the hotel, rose. "Your Honor, they proved he can't park on his own. They never showed that parking on your own makes your life better. Without that link, 'can't park' is just a fact, not a harm." The judge tapped her pen. "Counsel, you need that bridge."

Step 5 · Work the real question

Open PrepTest 116, Section 2, Question 23 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Map the chain: what does the first premise lead to, and what does that lead to? Note where the chain stops. Compare it to the conclusion and find the new idea that appears only there. Predict a bridge linking the last link to that new idea. Use the Pull the Plank test: negate the choice and see if the argument breaks. Watch for overly strong or overly broad choices.