Our beliefs guide our actions. But do potential actions also guide our beliefs? Three experiments tested whether people use pragmatist principles in fixing their beliefs, by examining situations in which the evidence is indeterminate between an innocuous and a dire explanation that necessitate different actions. According to classical decision theory, a person should favor a prudent course of action in such cases, but should nonetheless be agnostic in belief between the two explanations. Contradicting this position, participants believed the dire explanation to be more probable when the evidence was ambiguous. Further, when the evidence favored either an innocuous or a dire explanation, evidence favoring the dire explanation led to stronger beliefs compared to evidence favoring the innocuous explanation. These results challenge classic theories of the relationship between belief and action, suggesting that our system for belief fixation is sensitive to the utility of potential beliefs for taking subsequent action.