Intervening in key debates at the interface between syntax and semantics, this book examines the relation between structure and meaning in words. 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.