Research on spontaneous language acquisition both in children learning their mother tongue and in adults learning a second language has shown that language development proceeds in a stagewise manner. Learner utterances are accounted for in terms of so-called 'learner languages'. Learner languages of both children and adults are language systems that are initially rather simple. The present monograph shows how these learner languages develop both in child L1 and in adult L2 Dutch. At the initial stage of both L1 and L2 Dutch, learner systems are lexical systems. This means that utterance structure is determined by the lexical projection of a predicate-argument structure, while the functional properties of the target language are absent. At some point in acquisition, this lexical-semantic system develops into a target-like system. With this target-like system, learners have reached a stage at which their language system has the morpho-syntactic features to express the functional properties of finiteness and topicality. Evidence of this is word order variation and the use of linguistic elements such as auxiliaries, tense, and agreement markers and determiners. Looking at this process of language acquisition from a functional point of view, the author focuses on questions such as the following. What is the driving force behind the process that causes learners to give up a simple lexical-semantic system in favour of a functional-pragmatic one? What is the added value of linguistic features such as the morpho-syntactic properties of inflection, word order variation, and definiteness?

The book concerns theoretical, interdisciplinary and methodological issues in L2 acquisition research. It gives an accurate and up-to-date overview of high quality work currently in progress in research methodology, processing, principles and parameters theory, phonology, the bilingual lexicon, input and instruction. The volume will have the purpose of a handbook for teachers, students and researchers in the area of second language acquisition. The aim is to provide the reader with an acquisition perspective on processes of second and foreign language learning.

Language acquisition is a developmental process. Research on spontaneous processes of both children learning their mother tongue and adults learning a second language has shown that particular stages of acquisition can be discriminated. Initially, learner utterances can be accounted for in terms of a language system that is relatively simple. In studies on second language acquisition this learner system is called the Basic Variety (Klein and Perdue 1997). Utterance structure of the Basic Variety is determined by a grammar which consists of lexical structures that are constrained, for example, by semantic principles such as "The NP-referent with highest control comes first" and a pragmatic principle such as "Focus expression last". At some point in acquisition this lexical-semantic system is given up in favour of a target-like system with morpho-syntactic features to express the functional properties of finiteness, topicality, the determiner system, etc. Insights into how this process evolves may also provide an answer to the question of why it takes place. Within this functional perspective on language acquisition research focuses on questions such as the following. 1. What is the driving force behind the process that causes learners to give up a simple lexical-semantic system in favour of a morpho-syntactic functional category system? 2. What is the added value of morpho-syntactic properties of inflection, word-order variation, definiteness and agreement? 3. Why is it that in cases of specific language impairment it is mainly morpho-syntactic properties of the target language that are affected?

Acquisition of the native language proceeds in a stage-wise manner for both typically developing (TD) children and children with developmental language disorder (DLD). As shown in TD children learning Dutch and German, the ability to establish contextual cohesion serves as the driving force to proceed from a simple, lexical system to a more complex, functional system. It is argued that precisely this ability is challenged in children with DLD. The present book offers an account of the functional linguistic features fit to achieve contextual cohesion in language production. It provides a rationale for practitioners to develop linguistically founded tools to be used in speech therapy.