Modality is a category of linguistic meaning having to do with the expression of possibility and necessity. A modalized sentence locates an underlying or prejacent proposition in the space of possibilities (the term prejacent was introduced by medieval logicians). Sandy might be home says that there is a possibility that Sandy is home. Sandy must be home says that in all possibilities Sandy is home. The counterpart of modality in the temporal domain should be called temporality, but it is more common to talk of tense and aspect, the prototypical verbal expressions of temporality. Together, modality and temporality are at the heart of the property of displacement (one of Charles F. Hockett's design features of human language) that enables natural language to talk about affairs beyond the actual here and now.

There are numerous kinds of expression that have modal meanings, the following is...