It is often not apparent what people ought to do. Three experiments explored cues that children and adults may use to identify conventional obligations. Experiment 1 addressed the hypothesis that young children identify obligations with expected outcomes. Although preschool-aged (4-5 years) children often expected consistency, they and school-aged (7-8 years) and adult participants indicated that obligations may be at odds with costs and benefits. In Experiment 2, all participants realized that people may have obligations they are unaware of. Preschool-aged children often used information about obligations to identify characters' beliefs. In Experiment 3, preschool but not school-aged children reliably identified obligations with the desires of authorities. The results are discussed in terms of expectations about canonical relations between mental states, outcomes, and obligations.