No. 47 · Risk · Fallacy
Conjunction Fallacy
Every added detail makes a story more convincing and less likely.
In the Almanac
“The Linda problem”, 1983 · “Better Place”, 2007–2013
Both stories in full, three ways to use it and where it misleads.
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Questions
What is Conjunction Fallacy?
The conjunction fallacy happens when a detailed story feels more probable than a simpler one. Every added condition can only keep the odds the same or lower them, yet vivid detail makes outcomes feel more believable.
How do you avoid Conjunction Fallacy?
When a plan, forecast or worry depends on several things happening together, list each assumption and estimate it separately. Remember that the combined chance is always lower than its weakest single link.
When does Conjunction Fallacy matter?
Conjunction Fallacy is one of the 32 mental models for risk, the situations where you ask: What could go wrong, and what will I do if it does? Within that, it belongs to “Misreading chance”, alongside Availability Bias, Gambler’s Fallacy and Hot-Hand Fallacy.
What is an example of Conjunction Fallacy?
Two stories show it at work: The Linda problem (1983) and Better Place (2007–2013). Both are told in full in The Mental Models Daily Almanac, which has two stories for each of its 365 models.
Which mental models are related to Conjunction Fallacy?
Narrative Instinct, Hofstadter’s Law and Conditional Probability. Conjunction Fallacy itself comes from fallacy.