Bybee Joan L. Bybee & Fleischman Suzanne Fleischman 
Modality in Grammar and Discourse [PDF ebook] 

This volume brings together a collection of 18 papers that look into the expression of modality in the grammars of natural languages, with an emphasis on its manifestations in naturally occurring discourse. Though the individual contributions reflect a diversity of languages, of synchronic and diachronic foci, and of theoretical orientations — all within the broad domain of functional linguistics — they nonetheless converge around a number of key issues: the relationship between ’mood’ and ’modality’; the delineation of modal categories and their nomenclature; the grounding of modality in interactive discourse; the elusive category ’irrealis’; and the relationship of modal notions and categories to other categories of grammar.