Forms such as this one are often misconstrued as other modalities further modified (in this case, volition negated and modified for possibility). Imperative-hortative systems Many languages have imperative-hortative systems in which modalities dealing with commands and encouragement are grouped together. That is not the case in English and results in some disagreement among linguists. Imperatives and hortatives both involve the expression of a wish of the speaker about a future state of affairs. In that respect, they are like optatives, but in contrast to optatives, they convey an appeal to the addressee(s) to help make the future state of affairs true. If the person in control of the desired state of affairs is the addressee(s), the utterance is an imperative. In any other case, it is a hortative. Consider the following examples: May he live a hundred years! (optative) Sing! (imperative) Let's sing! (hortative) (1) illustrates an optative. It expresses a wish or hope of the speaker, but there is no appeal to the addressee to make it true. (2) and (3) also express a wish of the speaker, but in both cases, there is an appeal to the addressee to help make it true, with the desired future state of affairs specified as that of someone singing. Note that the person(s) supposed to sing is/are the addressee(s) in (2), thus making it a command. In (3), however, the intended singer(s) is/are the addressee(s) together with the speaker, thus effecting the modality of mutual encouragement that the speaker and the addressee(s) are to perform the action. References Sources Palmer, Robert L. Mood & Modality. Cambridge University Press, Cambridge. 2001 Palmer, Robert L. Modality & The English Modals. Longman, London. 1979 Grammatical moods