1. A method of recognizing natural language in a dialogue system, the method comprising: by at least one hardware processor interfaced with a memory including instructions which control the at least one hardware processor to: input voice data of a user; parse the voice data of the user to generate a parsed input set; determine whether the parsed input set is included in an initial domain including an initial input set generated before dialogue with the user and in an extended domain including an extended input set generated upon dialogue with the user; provide an understood result comprising content based on at least one of the initial input set and the extended input set according to a result of the determination; and output the understood result.