Natural language interface to a back-end application, incorporating synonyms, suggestions, and proposals. Roughly described, synonyms are automatically added to user input to enhance the natural language interpretation, whereas suggestions and proposals are offered to the user in an interaction, usually after an interpretation of prior user input. Suggestions and synonyms can be learned from user input, whereas proposals are programmed by a third party. The selection of synonyms, suggestions, and proposals for use with particular user input can be context-based, and rewards-based reinforcement can be used to better focus suggestions and proposals on the characteristics of the particular user.