The bilingual child does not fuse the two languages to which she is exposed; rather, in each language, most of the milestones she reaches, and even most of the errors she makes, align neatly with those of a monolingual acquiring that language. Hence it is generally agreed that the bilingual child acquires two separate grammars (e.g., Meisel, 1989, Genesee et al., 1995). Yet this separation does...