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Mind & biases2 MINBrief fileEstablished evidence

Conjunction Fallacy

A detailed story sounds persuasive. Can it be more likely than a broader version of that same story?

01 / SUMMARY

In short

The probability of A and B occurring cannot exceed the probability of A alone. Yet a representative description can make the more specific combination feel more plausible.

03 / SCENE

In the wild

“Works at a bank and is active in environmental causes” cannot be more common than “works at a bank,” because the first group sits inside the second.

04 / LIMIT

The limit

It is not an error to say the combined story fits better; the mistake is turning that fit into a higher probability.

FINAL NOTE

What remains

Draw the sets: if one option is contained within another, it cannot include more cases.

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Editorial review: 2026-08-06

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