Unit 8 · Detecting Reasoning Errors
Darryl and Jim — Spot the Reasoning Error
Lesson 1 of 10
Jim finds one blue hooded jacket and immediately says "it must be hers." His error: a description can match MORE THAN ONE object. Finding one match doesn’t prove it’s the only match — or the right one.
"False uniqueness" errors (assuming the first matching object is the only or correct one) appear consistently in OC TS Detecting Reasoning Errors questions. They are easy marks once students recognise the pattern: "matches the description ≠ must be THE specific one."
The examiner checks whether students can identify that Jim’s jump from "fits the description" to "must be hers" is unjustified — because descriptions are not always unique identifiers. The correct flaw is ambiguity of the description, not problems with Darryl’s instructions or Jane’s preferences.
Person A describes an item (colour + feature). Person B finds an item matching the description and declares it must be the one. Students identify which statement reveals the flaw in Person B’s reasoning.
Best approach: Ask: "What assumption did Jim make?" He assumed one matching object = the correct one. The flaw option must directly challenge that assumption. The correct answer will say the description could match multiple objects, making Jim’s conclusion unjustified.
Question
Darryl and Jim are in the corridor.
Darryl says: "Jane asked me to fetch her jacket, but I can’t seem to find it here. It’s blue, with a hood, she says."
Jim says: "Here’s a blue jacket with a hood — it must be hers!"
Which one of the following sentences shows the mistake Jim has made?
Select an answer to see the explanation.
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