principleintermediatemid level

Conjunction Fallacy

Judging a conjunction of two events (A and B) as more probable than one of the events alone (A), violating basic probability rules.

In Depth

The famous Linda problem demonstrates this: given a description of Linda as concerned with social justice, people judge 'Linda is a bank teller and active in the feminist movement' as more probable than 'Linda is a bank teller,' even though the conjunction cannot be more likely than its components. This occurs because the conjunction is more representative of the description—it 'fits' better. The representativeness heuristic overrides logical probability, revealing how System 1's pattern-matching can produce systematic errors in probabilistic reasoning.

Example

Investors judge 'The company will succeed AND expand internationally' as more likely than 'The company will succeed,' because the detailed scenario is more representative of success stories, even though it's logically less probable.

Common Misconception

More detailed scenarios are more likely—adding details always reduces probability, even when the details make the scenario more plausible or representative.

Source

Thinking, Fast and Slow

Daniel Kahneman

probabilitylogicdecision-making

Related Concepts

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Representativeness Heuristic

Judging probability by similarity to stereotypes or prototypes, while ignoring base rates and sample size.

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Representativeness Heuristic

Judging probability by similarity to stereotypes or prototypes, while ignoring base rates and sample size.

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Base Rate Neglect

Ignoring statistical base rates (how common something is in the population) in favor of specific case information or stereotypes.

Test Your Understanding

active recallhard

Why is judging 'Linda is a bank teller and active in the feminist movement' as more probable than 'Linda is a bank teller' a logical error?

applicationmedium

An investor evaluates two scenarios: (A) 'The company will succeed' versus (B) 'The company will succeed AND expand internationally.' Why might they judge B as more likely, and why is this problematic?