This paper presents a formal model of language acquisition that, in addition to meeting the traditional learnability condition, makes time-course predictions about child language development. We view language acquisition as a population of human grammars, made available by UG, compete in a selectionist process. Selection is made possible by the variational properties of individual grammars;
... [Show full abstract] specifically, their di#erential compatibility with the primary linguistic data in the environment. We first present developmental facts that are problematic for both a statistical learning approach and traditional learnability models. We then propose a formal model of acquisition in the variational framework, and derive some convergence results. The model receives empirical support from developmental evidence in child language, including the subject drop phenomenon, that a learner is best modeled as a population of grammars in co-existence and competition, rather than a single grammar suppl...