Conjunction Fallacy is believing a specific scenario is more likely than its more general one. It sits in the Cognition dimension (COG) of the Human Behavior Taxonomy™ as element HBT-COG-0177, within the Probability Bias family. The core principle: believing a specific scenario is more likely than its more general one. In incentive terms, it matters because it changes the payoff people perceive before they choose — which means it can be designed for, or exploited.
Scientific Definition
Believing a specific scenario is more likely than its more general one.
Plain-English Definition
Believing a specific scenario is more likely than its more general one.
Feynman Explanation
'Linda is a feminist bank teller' feels more likely than just 'Linda is a bank teller.' It can't be.
Core Principle
Believing a specific scenario is more likely than its more general one.
Mechanisms
Believing a specific scenario is more likely than its more general one.
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Inputs (Triggers)
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Outputs (Behaviors)
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Behavioral Signature
'Linda is a feminist bank teller' feels more likely than just 'Linda is a bank teller.' It can't be.
Examples
- Strategies sold as detailed scenarios that are necessarily less likely than the general bet.
- Forecasts that gain credibility by gaining unnecessary detail.
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Original analysis from The Incentives Lab — how this element behaves inside real payoff structures.
Why this element matters to incentive design
This is one of the elements leaders describe as a values gap. It is a payoff gap. The mechanism underneath it is straightforward: believing a specific scenario is more likely than its more general one. You can recognize it in the field by its signature: 'Linda is a feminist bank teller' feels more likely than just 'Linda is a bank teller.' It can't be. Every element in the Cognition dimension changes the perceived payoff of an action before the action happens, which is exactly where incentive design has leverage.
How it gets exploited
Left undesigned, aI predictions trusted more when narratively rich; that's the wrong signal. It is amplified whenever forecasts that gain credibility by gaining unnecessary detail. Inside organizations that shows up as forecasts that gain credibility by gaining unnecessary detail. The pattern is the same one Goodhart's Law describes: the measurable proxy attracts the effort, and the purpose behind it quietly loses funding.
How the Lab designs around it
The redesign move is to decompose claims into base probabilities. The leverage is not in explaining the behavior to people. It is in changing what the behavior earns.
Famous Experiments
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Design Principles
- Decompose claims into base probabilities.
Measurement Approaches
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Evidence
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The Perverse Incentive Lens™
How this behavior is exploited — and how to redesign around it.
- Decompose claims into base probabilities.
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Interactive Mini Network
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Knowledge Graph Neighbors
Auto-linked to the rest of the Human Behavior Taxonomy by family, domain, dimension, and shared keywords.
Believing past random events influence future independent ones.
Believing streaks predict future streaks.
We underestimate time and cost; we overestimate benefit.
We prefer known risks to unknown ones, even when the unknown is better.
We ignore underlying probabilities in favor of vivid specifics.
Underestimating the probability of bad outcomes — especially to us.
Overestimating the probability of bad outcomes.
Worst-cases assumed as base-cases because they 'feel responsible.'
We prefer eliminating a small risk completely over reducing a larger one partially.
Systematic deviations from rationality in judgment.
Throwing more in because we already threw a lot in.
Generalizing from winners while ignoring identical losers.
Where Conjunction Fallacy is cited in the corpus
Essays, field guides, and diagnostics from The Incentives Lab that apply this element.
- EssayGoodhart's Law in the Real World
How measurable proxies capture judgment.
- EssayThe Perverse Incentives Hiding in Your KPIs
Cognitive shortcuts turned into scorecards.
- CourseIncentives 101
The free ten-part primer on reading a payoff structure.
- ReferenceThe Periodic Table of Human Behavior
The full 1,267-element map this page belongs to.
Questions about Conjunction Fallacy
- What is Conjunction Fallacy?
- Conjunction Fallacy is believing a specific scenario is more likely than its more general one. It sits in the Cognition dimension (COG) of the Human Behavior Taxonomy™ as element HBT-COG-0177, within the Probability Bias family. The core principle: believing a specific scenario is more likely than its more general one. In incentive terms, it matters because it changes the payoff people perceive before they choose — which means it can be designed for, or exploited.
- What is an example of Conjunction Fallacy?
- Forecasts that gain credibility by gaining unnecessary detail. The Incentives Lab catalogs everyday, organizational, and historical instances of this element on its Human Behavior Taxonomy™ page (HBT-COG-0177).
- How is Conjunction Fallacy exploited?
- AI predictions trusted more when narratively rich; that's the wrong signal.
- How do you design around Conjunction Fallacy?
- Decompose claims into base probabilities.
- Which behavioral dimension does Conjunction Fallacy belong to?
- Conjunction Fallacy is classified in the Cognition dimension (COG) of the Human Behavior Taxonomy™, family "Probability Bias", class "Cognitive Bias". Its permanent identifier is HBT-COG-0177 and its evidence grade is B.