Variability, Its Limits, and the Performance–Competence Debate: Implications of Linguistic Variability for a Theory of Grammar

This article provides an overview of variability in natural language by looking at the limits of intraindividual, interindividual, and cross-linguistic variability at all levels of grammar. We review evidence for the hypothesis that variability forms an integral part of natural language and often provides valuable insights into speakers’ linguistic competence. We discuss in turn ( a ) different subtypes of variability; ( b ) the difference between systematic linguistic variability, as driven by grammar or processing-related factors, and random noise, including performance errors; ( c ) the phenomenon of hidden variability, where linguistic expressions can differ in their underlying structure despite parallel surface strings; ( d ) the extent to which variability is accounted for in existing grammatical theories; ( e ) variability in experimental quantitative data as a window into the underlying grammatical systems and processing mechanisms; and ( f ) variability in language as an important trigger for diachronic change and language acquisition.