The cross-overs between monolingual-bilingual and typically atypically developing children are a goldmine for research on language development. The four permutations of language exposure and language abilities create "natural experimental conditions" for investigating the nature of the language capacity and how this is shaped by input in typical development, and importantly, in specific language impairment (SLI). Paradis has played a prominent part in identifying and exploring this rich source of evidence. Her Keynote Article provides a valuable review of findings from her own and others' research, a carefully considered evaluation of their compatibility with competing theories of language development, and an excellent catalyst for debate.