A theory of construction grammar developed by William Croft.

Radical construction grammar (RCG) sets out to explore the implications of linguistic typology for syntactic theory. Linguistic typology is the sub discipline of linguistics that examines the structural properties of language from a cross-linguistic perspective and describes patterns of similarity as well as observing points of diversity. In RCG, rather than taking grammatical universals across the world's languages as a starting point and building a model of language that assumes a universal grammar (as in formal linguistics ), grammatical diversity is taken as the starting point. RCG attempts to build a model of grammar which accounts adequately for patterns of typological variation.

What makes Croft's constructional approach 'radical' emerges as a consequence of the typological stance he adopts. In RCG, the existence of constructions is the only primitive theoretical construct. All other linguistic elements, including word classes such as nouns and verbs, word order patterns and grammatical relations such as subject and object are epiphenomenal.

In this way, the notion of syntax, as usually understood, is eradicated from the theory altogether.