Overgeneralizing

Overgeneralizing is a reasoning error in which a judgment based on limited evidence is applied to a broad range of cases. It involves taking a single instance, a small sample, or a particular circumstance and extending it to an entire category, population, or situation, often ignoring important variations and exceptions.

Common forms include basing beliefs about a group on the behavior of a few members, or concluding that one negative experience predicts similar outcomes in all contexts. In logic, this pattern is related to the fallacy of hasty generalization, where insufficient data leads to a broad claim such as "All X are Y" or "Nothing ever goes right."

Causes include cognitive efficiency strategies (heuristics), emotional reactions, stereotypes, and confirmation biases that favor information confirming a preexisting belief. Overgeneralizing can contribute to prejudice, poor decision making, and distorted interpretations of events.

Countermeasures involve seeking representative evidence, acknowledging exceptions, using probabilistic language, testing hypotheses with data from diverse cases, and slowing down judgment when data are sparse. In education and critical thinking, recognizing this error helps improve reasoning and argument quality.