1. A method for sentence planning in a task classification system that interacts with a user, comprising: recognizing symbols in a user's single input communication to a task classification system; determining whether the user's input communication can be understood, wherein if the user's communication can be understood, understanding data is generated; generating a plurality of communicative goals based on the recognized symbols and understanding data, the generated plurality of communicative goals being related to information needed to be obtained from the user; in response to information from the user's single input communication: generating a plurality of sentence plans based on the plurality of generated communicative goals, each sentence plan in the plurality of sentence plans being a realization comprising elementary speech acts each corresponding to a respective communicative goal and combined into at least one complete sentence that accomplishes the plurality of communicative goals, and wherein each sentence plan of the plurality of sentence plans is a viable and potentially usable prompt in response to the user's single input communication; independent of the user, ranking the plurality of generated sentence plans; and outputting at least one of the ranked sentence plans to the user as a response to the user's single input communication such that one dialog turn occurs starting with the user's single input communication and ending with the outputted sentence plan.