Radical Construction Grammar presents a profound critique of syntactic theory and argumentation, and offers a genuinely new approach to syntax based on the fact of grammatical diversity. Recent syntactic theories are essentially formal models for the representation of grammatical knowledge and posit complex syntactic structures in the analysis of sentences. The result has been a endless cycle of new and revised theories of syntactic representation. Radical Construction Grammar argues that this approach to syntax is incompatible with the grammatical variation found within and across languages. This book defends three fundamental theses: (i) constructions are the primitive units of syntactic representation, and grammatical categories are defined by constructions, not the other way around; (ii) the only syntactic structures are the part-whole relations between a construction and the syntactic elements that make it up; (iii) not only are grammatical categories construction-specific, but constructions are language-specific. In other words, syntactic structure is almost entirely language-specific; attempts to find a universal formal model are doomed to failure. Radical Construction Grammar integrates concepts from typological theory and construction grammar to uncover the genuine universals of grammar. Constructions are represented as complex symbolic units pairing form and meaning. The semantic map model of typological theory is used to map category distributions on a largely universal conceptual space. Universals of grammar are found in the mapping of meaning onto form. Systematic patterns of grammatical variation provide evidence for the topography of conceptual space, which in turn reflects the geography of the human mind.