Age-related differences in human behaviour are central to developmental fields of research. Studies in psychology and the cognitive sciences have accrued an increasing body of evidence for changes across the life-span in areas such as brain plasticity, personality and behavioural patterns (Mühlig-Versen et al. 2012, Donnellan & Lucas 2008, Chang 2014 inter alia). Age-related changes in the grammar of the individual speaker, on the other hand, are still largely overlooked and ignored. The main reason can be found in a core schism within the field of the language sciences. Formal schools of linguistics dismiss the notion that changes in internal grammar can occur post critical age (Sobin 1997, Lightfoot 1999, Anderson 2016). Usage-based strands of linguistics, on the other hand, tend to take life-span change for granted "as the perceptual memories associated with a category accumulate" (Gahl & Yu 2006:214). Consequently, little research has explored the theoretical implications of episodic experience across the adult life-span. Only recently have functionally-orientated linguists started to systematically assess the nature and the generalizability of the critical period in speaker grammars (Sankoff & Blondeau 2007). While an ever-growing body of studies have documented intra-speaker malleability in post adolescence, to date, we lack a coherent model of the "relative stability of people's grammar in adult life" (Sankoff 2013a:261). The present project aims to:

1. systematically explore language variation and change within the individual speaker across a panel sample of speakers ages 18-65,
2. use this knowledge-base in order to explore how intra-speaker lability articulates with the community grammar (Guy 1980), and to
3. assess the consequences of post-adolescent malleability for our models of language change.

The first aim is met by collating a unique dynamic data-base which allows the investigation of linguistic (in)stability over the entire adult life-span. The LaVaLi project addresses the second aim by applying cutting-edge statistical techniques to explore the contingent nature of intra-speaker malleability at different levels of linguistic architecture. The project results will significantly advance our understanding of the role of maturational effects and life experiences in shaping individual patterns of behaviour. As such, the LaVaLi project will inform the debate about the range and the determinants of post-adolescent linguistic malleability (Bowie & Yaeger-Dror 2015:608).