In 1939, NYU Professor of German, Murat Roberts warned readers about the potentially harmful effects of societal bilingualism: “When two languages come to be spoken by the same society for the same purposes, both of these languages are certain to deteriorate. The sense of conflict disturbs in both of them the basis of articulation, deranges the procedure of grammar, and imperils the integrity of thought. The representation of the mind is divided into incongruous halves; and the average speaker, being no linguistic expert, finds it difficult to keep the two media apart. Confusion follows. The contours of language grow dim as the two systems collide and intermingle” (23). Roberts’ warnings about the threat of bilingualism are a thin cloak over the assumption that monolingualism is the norm. But even without dire predictions, conceptions of language representation and use derived from the study of bilinguals have been slow to enter the mainstream. The relation between language representation and control (Abutalebi & Green, 2007) and the dynamic nature of grammatical knowledge across the lifespan (Linck, Kroll & Sunderman, 2009) should change the way we conceptualize all language processing, whether monolingual, bilingual or multilingual.