Conjunction fallacy is demonstrated when someone:

• A. Believes that a conjunction is more probable than a single component
• B. Believes that a single component is less probable than a conjunction
• C. Confuses correlation with causation in a single event
• D. Ignores base rates when judging probabilities

Answer: (A)

The conjunction fallacy happens when people treat a conjunction as more probable than one of its individual parts. In probability, the chance of both events happening (A and B) cannot exceed the chance of either one alone. Yet, when a description feels highly representative of a person or scenario, people often judge the combined description as more likely, even though it’s mathematically less probable.

In this question, the best description is that someone believes a conjunction is more probable than a single component, which is exactly the conjunction fallacy. The other ideas describe different biases (such as mistaking correlation for causation or ignoring base rates), which aren’t the same fallacy.