One of the major arenas for debate within generative grammar is the nature of paradigmatic relations among words. Intervening in key debates at the interface between syntax and semantics, this book examines the relation between structure and meaning, and analyzes how it affects the internal properties of words and corresponding syntactic manifestations. Adapting notions from the Evo-Devo project in biology (the idea of 'co-linearity' between structural units and behavioural manifestations) Juan Uriagereka addresses a major puzzle: how words can be both decomposable so as to be acquired by children, and atomic, so that they do not manifest themselves as modular to adults.