1. A method comprising, by a computing device: receiving, from a client system of a first user of an online social network, a first structured query comprising a natural-language string generated by a grammar model and references to one or more objects associated with the online social network; generating one or more query modifications for the first structured query, each query modification comprising references to one or more modifying objects associated with the online social network; and sending, to the client system of the first user, one or more of the query modifications as suggested modifications to the first structured query for display to the first user, each query modification being selectable by the first user to modify the natural-language string of the first structured query to further comprise references to the one or more of the modifying objects referenced in the selected query modification.