8. A system comprising: a processor; and a computer-readable storage medium storing having instructions stored which, when executed on the processor, cause the processor to perform operations comprising: identifying segments of a dialog system based on a timing of probable user responses; exclusively activating a weighted grammar for a specific segment of dialog in the dialog system during the specific segment of the dialog turn, to yield an activated weighted grammar; and recognizing user speech received during the specific segment of the dialog using the activated weighted grammar.
8. A system comprising: a processor; and a computer-readable storage medium storing having instructions stored which, when executed on the processor, cause the processor to perform operations comprising: identifying segments of a dialog system based on a timing of probable user responses; exclusively activating a weighted grammar for a specific segment of dialog in the dialog system during the specific segment of the dialog turn, to yield an activated weighted grammar; and recognizing user speech received during the specific segment of the dialog using the activated weighted grammar. 9. The system of claim 8 , the computer-readable storage medium having additional instructions stored which result in operations further comprising assigning a probability to the weighted grammar based on historical user responses and activating the weighted grammar based on the probability.