Feature values and the expression of variation
This paper proposes that feature values emerge dynamically from the interaction between features and the internal/structural and language-external environments. Feature values constitute a second, flexible layer around a selected sub-set of innate features, and effect linguistic variation within dialects and typologically related languages. Big, structural changes however originate from restricted changes in feature composition themselves, often the result of adding a new feature to the language-particular sub-set or repurposing some existing feature. Relevant analogies with biological variation are discussed in favor of the multi-level approach to linguistic variation proposed here.