Variation is a prominent ingredient of language as it presents itself to us. Languages differ from each other in various respects, e.g., in their sentence structure (syntax), word structure (morphology), sound structure (phonology) and vocabulary (lexicon). However the extent and limits of variation are a challenging puzzle.
Another characteristic of human language is that it is dynamic. Languages change over time. As a result, linguistic properties need not be stable. For a proper understanding of language variation and language change, as manifest in the formal structure of human languages, we combine three perspectives:
The formal grammatical perspective
We study the ways in which linguistic diversity is encoded in the cognitive computational system that generates language structures, i.e. grammar.
Questions include: to what extent is linguistic diversity restricted by the grammatical blue print (Universal Grammar) underlying human languages? Where in the grammar are different dimensions of linguistic diversity encoded? Is the encoding of small linguistic differences (microvariation) fundamentally different from the encoding of major linguistic differences (macrovariation)? And, which parts of human language structure are invariant (i.e., universal) and how are these invariant properties encoded in UG?
We address the question how language variation exists and develops/changes in societies in which there is interaction between individuals and between groups speaking different languages/varieties. Research questions are: How and why do new language varieties arise in language contact situations, and how stable are these varieties? Under what circumstances will languages be under pressure and close to disappearance? What are the consequences of multilingualism and language contact for a linguistic community, and for the individual speaker?
The diachronic perspective
This perspective identifies the historical sources of linguistic divergence and convergence: how and why have related languages grown apart? How did features shared by unrelated languages arise?
Research focusing on these three perspectives jointly, allow us to address the central question: how do internal factors (grammar) and external factors (linguistic and social interaction in linguistic communities, and the factor time) interact, and what is their role in linguistic diversity and change.