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Conjunction fallacy

Judging a combination of events as more likely than one of its component events.

Published 04 August 2026Updated 04 August 2026

The conjunction fallacy occurs when a detailed, coherent scenario feels more probable than a broader event that includes it. Because every A-and-B case is also an A case, the conjunction cannot be more likely than A alone.

Sources

Judgment under Uncertainty: Heuristics and Biases

Science / 1974 / Paper

Classic heuristics and biases paper.