Logical Reasoning · Flaw

PrepTest 136 · Section 2 · Question 1

Phase 1 (your first ~400 questions): read the guidance, then answer. No clock.

Step 1 · Pre-Question Guidance · read this first

Question type

Flaw

The one idea it tests

An argument that offers only two paths and never explains why every other path is off the table.

The basic logic

Find the either/or setup. Ask: who said these are the only choices? If one door is knocked down and the other is declared the winner, while a third door was never checked, you have Only Two Doors.

Tiny words that decide it

“either ... or”
“only choice”
“therefore”

Playground logic

Marcus builds a burger where the patty is 'we either buy a goldfish or the tank stays empty forever,' and 'an empty tank is sad.' His top bun is 'buy the goldfish.' The secret sauce he never shows us is that those were the only two doors, when a turtle or a snail was waiting in the hallway the whole time.

Step 2 · The kid story

The Great Fish Tank Vote

Ms. Rivera's class has an empty fish tank in the corner. Marcus climbs on a chair like a mayor. "Friends, we have two choices," he announces. "We get my goldfish, Captain Bubbles, or this tank sits empty until we all graduate." He points at the dusty glass. "An empty tank is gloomy. Nobody wants gloomy. So we vote for Captain Bubbles!" Kevin claps, then asks if a dinosaur fits in a tank. Priya sips her juice box and raises her hand. "Marcus, why only two choices? We could get a snail. We could grow water plants. We could borrow Nadia's hermit crab." Marcus blinks. "Well, those are... also choices." Lulu writes on her clipboard: two doors shown, more doors in the hallway, zero reasons given for skipping them.

Step 3 · Try the model question

Marcus: Either the class adopts my goldfish or the tank stays empty until graduation. An empty tank would make the room gloomy, and nobody wants that. So the class should adopt my goldfish.

Marcus's reasoning is most open to which criticism?

Step 4 · The courtroom tale

The Case of the Two Bake Sale Tables

Mr. Whitfield snaps his suspenders. "Your Honor, the school must either use my client's purple tablecloth for the bake sale or use no tablecloth at all. No tablecloth means crumbs everywhere. Therefore, purple it is." Judge Okafor peers over her glasses. "Counsel, the supply closet has a green one, a striped one, and a roll of paper." Mr. Whitfield coughs. "Those were... not in my opening." "Exactly," says the judge. "You showed me two doors and nailed the others shut without a single reason. Knocking down one door does not crown the other. Motion denied, and please fold the purple one neatly."

Step 5 · Work the real question

Open PrepTest 136, Section 2, Question 1 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Read the stimulus and underline the either/or setup. Ask whether the speaker ever explains why those are the only paths. Notice that knocking out one path does not prove the other unless no third path exists. Then look for the choice that says the speaker offers just two paths and never explains skipping the rest. Skip choices that complain about details the argument never raised.