Judging a conjunction of two events (A and B) as more probable than one of the events alone (A), violating basic probability rules.
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.
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.
More detailed scenarios are more likely—adding details always reduces probability, even when the details make the scenario more plausible or representative.
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?
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?
Logically equivalent choices produce different decisions when framed differently (as gains vs. losses, or with different reference points).
PrincipleContinuing an endeavor because of previously invested resources (time, money, effort) that cannot be recovered, even when continuing is irrational.
PrincipleFast, automatic, unconscious cognitive processing that operates through pattern recognition and associative memory without deliberate effort.
Mental ModelSlow, effortful, conscious cognitive processing required for complex calculations, unfamiliar tasks, and deliberate reasoning.
Mental ModelThe tendency to rely too heavily on the first piece of information encountered (the anchor) when making decisions, even when it's arbitrary or irrelevant.
PrincipleJudging the frequency or probability of events by how easily examples come to mind, leading to overestimation of vivid, recent, or emotional events.
PrincipleJudging probability by similarity to stereotypes or prototypes, while ignoring base rates and sample size.
PrincipleWhen faced with a difficult question, System 1 automatically substitutes an easier question without conscious awareness of the switch.
FrameworkJudging a conjunction of two events (A and B) as more probable than one of the events alone (A), violating basic probability rules.
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.
More detailed scenarios are more likely—adding details always reduces probability, even when the details make the scenario more plausible or representative.
Conjunction Fallacy is explored in depth in "Thinking, Fast and Slow" by Daniel Kahneman. Distilo provides a deep AI-powered analysis with key insights, audio narration, and practical frameworks.