During language comprehension we must rapidly determine the thematic roles of arguments (who did what to whom) in order to semantically integrate the players into a single event and predict upcoming structure. While some languages signal these relations mostly with reliable word order, others rely more on case markers. The present study explores whether Turkish-speaking children use case marking predictively during online language comprehension. Specifically, we use the visual world paradigm to test whether 4-year-olds (and adults) can use a contrast between nominative and accusative case on the first noun to predict the referent of the second noun in verb-medial and verb-final spoken sentences. In verb-medial sentences, both children and adults used case to predict the upcoming noun, but children did so only after hearing the verb. In verb-final structures, however, both children and adults made predictive looks to the correct referent prior to the second noun (and the verb). Thus, Turkish-speaking preschoolers interpret case marking incrementally, independent of the verb, and use it to anticipate the upcoming argument. These findings are inconsistent with the hypothesis that the online interpretation of case marking depends on a late maturing neural circuit. The predictive use of case at four provides strong evidence that children's comprehension relies on broad, abstract mappings between syntax and semantics, which allow children to determine the event role of a case marked argument prior to identifying the verb.