Previous studies have shown that children have difficulty inferring intended referents of definite/indefinite determiners: e.g., that "Give me the ball" implies a specific ball, while "Give me a ball" requests any ball from a larger set. Here, we show that these findings need not indicate a fragile capacity for pragmatic reasoning because adults only make such inferences within specific contexts. Across four studies, we found that when presented with novel labels in definite contexts (the dax), adults consistently selected unique objects as the referent (though they were not at ceiling), suggesting they interpreted the definite as conveying specificity. Strikingly, however, when presented in indefinite contexts (a dax), subjects did not reliably link novel labels to objects of a larger set of kind-members, unless the context explicitly encouraged them to reason about the intended addressee. Together, these findings suggest that failures to make inferences about definiteness need not reflect pragmatic incompetence.