Logical Reasoning · Flaw

PrepTest 116 · 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

Knowing what starts something is not the same as knowing everything that controls how big it gets.

The basic logic

The patty says one force is the only cause of an event. The top bun jumps to: that force alone explains the size of the event. Look for the ignored helpers: surroundings or conditions that shape how strongly the cause works.

Tiny words that decide it

“only”
“entirely”
“must”

Playground logic

Marcus's patty: heat is the only thing that pops popcorn. His top bun: so heat alone decides how big each popped kernel gets. The secret sauce he never checked is that the kernel's own condition can change what the heat does, so he slides from 'what causes it' to 'what explains all of its size.'

Step 2 · The kid story

Marcus and the Great Popcorn Theory

Movie night at Priya's house. Marcus held up a giant fluffy kernel and a tiny shriveled one. "Detective fact," he announced. "The only thing that makes popcorn pop is heat. So how big a kernel gets is explained entirely by heat. Case closed." Priya sipped her juice box. "Heat starts the pop, sure. But some kernels were in the old bag that sat open all summer. They dried out. Same pan, same heat, smaller pops." Lulu wrote on her clipboard: Cause of popping = heat. Size of popping = heat PLUS what the kernel is like. Marcus frowned at the shriveled kernel. "So the heat is the boss, but the kernel gets a vote?" "Exactly," said Priya. "Knowing what starts it is not knowing everything that shapes it."

Step 3 · Try the model question

Marcus: Heat is the only thing that makes popcorn pop. Therefore, how big each popped kernel gets has to come down to heat and nothing else.

Which one of the following best describes an error in Marcus's reasoning?

Step 4 · The courtroom tale

The Case of the Lopsided Snowman

Judge Patel peered at two photos of snowmen. Mr. Whitfield snapped his suspenders. "Your Honor, the only thing that makes snow pile up is snowfall. So the size of each snowman is explained entirely by how much snow fell." The opposing lawyer stood. "Your Honor, both snowmen were built during the same storm. One was in the sunny front yard, one in the shady back yard. The snowfall started both piles. The conditions decided how much stayed." The judge nodded. "Counselor, you have shown what starts the pile. You have not shown it is the only thing that shapes the pile." Mr. Whitfield sat down slowly. "I may need a bigger theory, Your Honor."

Step 5 · Work the real question

Open PrepTest 116, Section 2, Question 1 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Find the top bun and notice how strong it is: does it claim one thing explains everything about the result? Then find the patty: it only says what triggers the result. Ask what else could change how strongly that trigger works, such as where or under what conditions it acts. Pick the choice that names the overlooked conditions. Skip choices that describe a move the argument never makes, or that complain about something the argument never needed.