Linguistic distance and crosslinguistic influence in the L2 and L3 acquisition of morphosyntax

In this introduction to the special collection on linguistic distance and crosslinguistic influence in second and third language acquisition, we contextualize the articles of the collection in current debates. We propose a three-tiered framework for typological comparison: individual feature similarity, parameter-setting similarity, and grammar-level linguistic distance. We review key theoretical debates in generative second language acquisition (SLA) regarding whether second language (L2) acquisition entails parameter resetting or feature (re)assembly, highlighting ongoing difficulties with functional morphology despite successful acquisition of syntactic word order. We connect recent large-scale empirical studies showing robust effects of linguistic distance on L2 outcomes with smaller experimental studies examining specific morphosyntactic features. The articles in the collection address four key questions: whether broad typological effects can be distinguished from feature-level effects; whether L1-L2/3 typological similarity consistently facilitates acquisition; how linguistic similarity should be measured; and how prior knowledge effects vary across proficiency levels. After introducing each article, we synthesize findings showing that broad typological effects often override individual feature similarities in determining transfer patterns. In contrast, linguistic proximity can sometimes impede acquisition when micro-variation requires costly ‘restructuring’ of existing first language (L1) representations rather than the development of a new item in L2. Large-scale studies reveal that lexical and morphological distance measures are more predictive than phonological or syntactic ones, with distance effects persisting across proficiency levels while, at the same time, shifting in relative importance during acquisition. We propose that considering multiple levels of typological granularity is essential for understanding crosslinguistic influence in multilingual development.