Chapter 3 explores cross-linguistic influence and various theories thereof in multilingual settings in which more than two languages interact with one another. It is specifically interested in the direction and strength of such influence, contingent on parameters like age of onset, proficiency, L1 and L2 status, linguistic and typological proximity, recency of use, language dominance, as well as various others. It identifies cross-linguistic influence as the more encompassing concept in comparison to the traditional notion of transfer widely used in second language acquisition studies. It also discusses the relationship between cross-linguistic influence and language interdependence, as proposed in education studies. While language interdependence builds on the proficiency-enhancing qualities of multilingualism (qua metalinguistic awareness), cross-linguistic influence can be both facilitative and inhibitory, the latter manifesting itself as interference. Crucially, non-facilitative transfer only arises within a normative system. Moreover, the mechanisms underlying cross-linguistic influence show important parallels to those identified in language contact studies with its focus on contact-induced language change.

The aim of this chapter is to offer the reader a panoramic yet comprehensive view of the theoretical issues and models that have attracted the most attention within generative approaches to L3/Ln morphosyntactic acquisition, with a particular emphasis on how transfer selection from previously acquired languages is hypothesized to apply. To the best of our ability, all models will be treated in an equal fashion. This does not mean that the description of each model will have or could possibly have the same level of detail, for justifiable reasons. To begin, models have appeared at different times, which correlates with more or less temporal opportunity to have been tested and to have gathered a critical mass of evidence. Moreover, not all models have had an equal amount of support from the published literature – a detailed analysis of which is the focus of Chapter 5 – and/or have had the same level of updating by their authors over time.