Logical Reasoning · Flaw

PrepTest 155 · 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

Flaw

The one idea it tests

Things that are needed for a result are treated as if having them guarantees the result.

The basic logic

The rule says: without these conditions, no result. The argument shows the conditions are met and concludes the result will happen. That is the Flipped Switch: a "needed" list was treated as a "guarantee" list.

Tiny words that decide it

“if not”
“then not”
“hence”

Playground logic

Marcus says kites without a long tail and strong string won't fly, notes his kite has both, and declares it will fly. Those parts were needed, not enough. His Flipped Switch ignores everything else a kite needs.

Step 2 · The kid story

Marcus's Unstoppable Kite

Marcus holds up his homemade kite. "Rule of kites: if a kite doesn't have a long tail and a strong string, it will not fly. Mine has the longest tail in town and the strongest string Grandpa owns. Therefore, my kite will fly!" Priya sips her juice box. "Marcus, your rule only says what kites need. It never says those two things are enough. What about wind? What about the frame?" Marcus lifts the kite. There is no wind. The frame is made of spaghetti. The kite flops onto Biscuit, who wags happily. "Detective Marcus," Lulu writes on her clipboard, "confused 'needed' with 'enough.'"

Step 3 · Try the model question

If a kite lacks a long tail and a strong string, it will not fly. Marcus's kite has a very long tail and a very strong string. So Marcus's kite will fly.

Marcus's reasoning is flawed because it

Step 4 · The courtroom tale

The Case of the Guaranteed Soufflé

A baker sued a cooking school, saying its class promised a perfect soufflé. Her lawyer read the brochure: "If you do not use fresh eggs and a hot oven, your soufflé will not rise." She said, "I used fresh eggs and a hot oven, so mine should have risen!" Mr. Whitfield, for the school, adjusted his suspenders. "Your Honor, the brochure lists things a soufflé needs. It never promises those things are enough. Whipping, timing, and not slamming the oven door also matter." The judge peered at the brochure. "Needed is not the same as enough. Case dismissed." The baker sighed, then asked Mr. Whitfield for whipping tips.

Step 5 · Work the real question

Open PrepTest 155, Section 2, Question 8 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Translate the opening rule into a conditional and note which part is the needed condition. Then check what the argument does: it shows the needed conditions are present and concludes the result. Match that to an answer that describes treating required conditions as sufficient ones. Ignore choices naming sample, cause, or word-meaning problems unless the argument actually does those things.