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
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?