Systems and processes for discourse input processing are provided. In one example process, a discourse input can be received from a user. An integrated probability of a candidate word in the discourse input and one or more subclasses associated with the candidate word can be determined based on a conditional probability of the candidate word given one or more words in the discourse input, a probability of the candidate word within a corpus, and a conditional probability of the candidate word given one or more classes associated with the one or more words. A text string corresponding to the discourse input can be determined based on the integrated probability. An output based on the text string can be generated.