Child and adult speakers of English have different ideas of what "or" means in ordinary statements of the form "A or B". Even more far-reaching differences between children and adults are found in other languages. This tells us that young children do not learn what "or" means by watching how adults use "or". An alternative is to suppose that…

According to the theory of Universal Grammar, the primary linguistic data guides children through an innately specified space of hypotheses. On this view, similarities between child-English and adult-German are as unsurprising as similarities between cousins who have never met. By contrast, experience-based approaches to language acquisition…