Logical Reasoning · Necessary Assumption

PrepTest 136 · Section 2 · Question 4

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 a slow method causes an inner change that goes along with improvement, a shortcut to that inner change only works if the improvement comes through that change.

The basic logic

The patty: a method produces change X, and X matches the good result. The top bun: a direct route to X will work just as well. The secret sauce: the good result comes by way of X, not through some other path the method also opens. Pull the Plank: if the method helps in some other way too, the shortcut falls short.

Tiny words that decide it

“only through”
“just as”
“eventually”

Playground logic

Reading lots of books grows Kevin's vocabulary, and bigger vocabulary goes along with better quiz scores. So Marcus says flashcards that pump up vocabulary will work just as well as reading. The secret sauce: the quiz gains come only through the vocabulary, not from other things reading builds.

Step 2 · The kid story

Flashcards Versus Books

Kevin has been reading dinosaur books every night for a month. His vocabulary has exploded. He says 'herbivore' at breakfast. His reading quiz scores have gone up too. Marcus slaps the table. "I've cracked it! Reading gives you new words, and new words match better scores. So we skip the books and just use word flashcards. Same results, way faster!" Priya sips her juice box. "That only works if the score boost comes entirely from the new words. What if reading also trained Kevin to follow a story, or to sit still for ten minutes? Flashcards don't do that." Marcus pauses. "So my shortcut needs the words to be the whole reason?" "Exactly," says Priya. Lulu writes: shortcut needs the middle step to be the only road.

Step 3 · Try the model question

Marcus: Reading many books builds a bigger vocabulary, and a bigger vocabulary matches better reading quiz scores. So kids will eventually raise their scores just as much with vocabulary flashcards as with all that reading.

Marcus's argument requires which assumption?

Step 4 · The courtroom tale

The Case of the Instant Garden

A salesman testifies that his Glow Spray turns any lawn green in a day. "Watering makes grass greener, and greener grass is healthier grass. My spray makes it green directly. Same health, no hose!" Mr. Whitfield stands. "Does watering do anything besides change the color?" "Well, it also feeds the roots," the salesman admits. "Then your spray only matches watering if the health comes entirely through the color," says Mr. Whitfield. "If the roots matter, painting the leaves green won't save the lawn." The judge nods. "The argument needs the middle step to be the only road. It isn't."

Step 5 · Work the real question

Open PrepTest 136, Section 2, Question 4 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Identify the method, the inner change it produces, and the good result that change goes along with. Then find the conclusion that a direct route to the inner change will work as well as the method. Ask what must be true for the shortcut to match: the good result has to come through that inner change alone. Use Pull the Plank on each choice: the right one, when negated, leaves the shortcut unable to match the method.