The present invention provides a dialogue system in which semantic ambiguity is reduced by selectively choosing which semantic structures are to be made available for parsing based on previous information obtained from the user or other context information. In one embodiment, the semantic grammar used by the parser is altered so that the grammar is focused based on information about the user or the dialogue state. In other embodiments, the semantic parsing is focused on certain parse structures by giving preference to structures that the dialogue system has marked as being expected.