Logical Reasoning · Necessary Assumption

PrepTest 141 · Section 2 · Question 8

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

An example is offered to show something is built to fit its user's needs. That only works if the user actually needs exactly what the thing delivers.

The basic logic

The conclusion says the design matches what the user needs, not what is ideal. The evidence shows a part that could do more, held back to do less. The secret sauce: the user needs only the 'less.' Pull the Plank: if the user needs more, the example shows a mismatch, not a fit.

Tiny words that decide it

“only”
“needs”
“not”

Playground logic

Aunt Rosa's bike has fancy gears, but the chain only reaches two low gears. She says bikes are set up for the rider's needs. That only works if Kevin, the rider, needs just those low gears.

Step 2 · The kid story

Kevin's Two-Gear Bike

Kevin's hand-me-down bike has a shiny ten-gear set on the back. But Aunt Rosa adjusted the chain so it only reaches the two lowest gears. Marcus is outraged. 'Ten gears and you can only use two? That's a broken bike!' Aunt Rosa smiles. 'This bike shows that bikes get set up for what the rider needs, not for some fancy idea of the perfect bike.' Priya thinks it through. 'That only works if Kevin really just needs the low gears.' Aunt Rosa nods. 'He rides up Dinosaur Hill to school and back. Low gears are all he uses.' Lulu writes: if Kevin needed fast gears, this bike would show the opposite. Kevin is too busy humming a stegosaurus song to notice any of it.

Step 3 · Try the model question

Aunt Rosa: Kevin's bike has a ten-gear set, but the chain is adjusted so only the two lowest gears work. This shows that bikes are set up to fit what their riders need, not to match some idea of a perfect bike.

Aunt Rosa's argument depends on assuming which one of the following?

Step 4 · The courtroom tale

The Mayor's Small Bridge

A builder sued the town. 'Your Honor, my company designed a bridge strong enough for trucks. The town only paved one narrow lane, wide enough for bicycles. What a waste!' The town's lawyer replied, 'This shows the town builds for its residents' needs, not for some perfect bridge.' Judge Feld leaned in. 'Counselor, your example works only if your residents need nothing more than a bicycle lane. Do they?' 'Yes, Your Honor. The island has no cars. Everyone bikes.' 'Then the narrow lane fits their needs,' the judge said. 'If trucks needed to cross, your example would prove the opposite.' The builder's case was dismissed.

Step 5 · Work the real question

Open PrepTest 141, Section 2, Question 8 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Identify the conclusion: something is shaped by what its user needs. Then look at the example: a capability that is present but held back. Ask what must be true for that example to show a fit with needs. The user must need just the reduced level. Pick the choice that says so, and test it with Pull the Plank: negate it, and the example should stop supporting the conclusion. Ignore choices about other species, history, or what would be nice to have.