Unit 8 · Detecting Reasoning Errors

Jake and Robert — Spot the Reasoning Flaw

Lesson 5 of 34

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About this lesson

Jake is going to the party; Robert is not. Natalie concludes Robert didn't do his homework. Daniel concludes Jake did. One of them has made a classic logic error — can you spot who?

Chapters

0:00Introduction
0:22Question
1:03Strategy
1:32Step 1: Write the rule and contrapositive
1:59Step 2: Check Natalie — inverse fallacy
2:26Step 3: Check Daniel — pick the answer
3:14Correct answer

Question

Jake and Robert are brothers. Their parents have told them that they will not be allowed to go to the party tonight if they have not completed their homework.

Natalie: "Jake is coming to the party, but Robert is not, so Robert can't have completed his homework."

Daniel: "Jake must have completed his homework."

If the information in the box is true, whose reasoning is correct?

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