Lexeme classes and word classes in functional discourse grammar

The approach to parts of speech in Functional Discourse Grammar (FDG) originates in the functional definitions of Nominal, Verbal, and Adjectival predicates in Simon C. Dik’s Functional Grammar. Kees Hengeveld’s later development and refinement of those ideas have been formalized within FDG as a theory of four functionally differentiated lexeme classes (Verb, Noun, Adjective, Adverb). These are distinguished from word classes, which may be more numerous and apply at the Morphosyntactic Level of FDG. Certain languages lack one or more lexeme classes; these are classified as either flexible or rigid. The resultant classification has been shown to determine word order, morphological type, and dependent clause constructions, and has strongly impacted the debate on parts of speech in language typology.