As explained in the introductory chapter, this book aims to make strides towards a model of language contact able to integrate its synchronic and diachronic manifestations, interpret societal innovations in the light of individual choices, and establish generalizations about the resistance of various structural components and grammatical categories to contact-induced change. The perspective taken here is essentially functionalist, as it considers the relevance of communicative settings and the agency of multilingual individuals in the process and end-result of language contact.

Ch. 2 is an ontogenetic study charting the emergence of a multilingual repertoire in a trilingual child. It describes the acquisition not only of linguistic items, but also of context-sensitive selection and co-selection restrictions that gradually associate the acquired items into “systems.” Ch. 3 starts by exploring how a multilingual repertoire is managed in the real world of communication, both at the microlevel (the way speakers map their linguistic systems onto specific settings) and the macrolevel (the mechanisms by which particular settings come to cue certain registers, and how this correspondence may change), and goes on to explore issues that arise in the context of the co-existence of languages in a given community such as bi-/unidirectional multilingualism, community-level maintenance/shift, and language policy. Ch. 4 reviews several theoretical approaches to the emergence of child bilingualism and considers the similarities and differences between it and second language acquisition, taking up the issue of the mental representation of multilingual knowledge.

Code-switching, in its various formal and functional types, is given ample coverage in Ch. 5. Borrowing (or copying or replication), interpreted as one of the ends of a continuum linking it to code-switching, is considered in Ch. 6 in terms of its sociolinguistic preconditions and motivations. Matras distinguishes here between “matter replication” (roughly, the borrowing of forms) and “pattern replication” (roughly, the borrowing of constructions; see below). The following chapters tackle “matter replication,” namely the borrowing of various types of lexical items (Ch. 7) and bound/unbound/semibound grammatical items (Ch. 8), surveying their borrowability and describing different strategies with regard to their structural integration into the recipient language. Ch. 8 also discusses instances of phonological replication, noting that the effect of language contact on the phonological systems of the languages involved may range from nil (i.e. integration of borrowed forms) to extreme (i.e. convergence of phonological systems). In the following chapter, Matras describes “pattern replication”, or the application of borrowed combinatory principles (syntactic, morphological, semantic, etc.) to recipient-language forms; the concept is then articulated with such diachronic phenomena as grammaticalization, convergence, and the emergence of linguistic areas. Ch. 10 consists of a brief survey of the formation and characteristics of contact languages (pidgins, creoles, mixed languages).

The final chapter draws some conclusions, namely concerning (i) the multilingual speaker's linguistic repertoire, said to constitute a holistic body of knowledge organized into permeable “systems” on the basis of acquired principles of context-appropriateness; (ii) the role of multilingual speakers, whose instances of conscious or unconscious system “interference” potentially trigger language change (subject to societal licensing); and (iii) the layered architecture of the language faculty, revealed by the fact that different components of grammar and structure are affected differently by language contact.