What makes a good explanation? We show that individuals prefer explanations with a more narrow scope – those that account for fewer unobserved effects – to broader explanations. In Experiments 1 and 2, participants evaluated a narrow scope and a broad scope explanation of an observed symptom and preferred the former to the latter. In Experiment 3, participants evaluated more natural explanations of unexpected observations, and again displayed a bias for narrow scope explanations. We conclude by considering what this novel bias tells us about how humans evaluate explanations and engage in causal reasoning.