Modelling Language Contact in <i>Magna Graecia</i> : Parameter Hierarchies, the Catapult Effect and Layering

Abstract This article explores a number of case studies taken from an exhaustive examination of Greek–Romance contact in southern Italy. Among other things, it highlights the relevance of the Greek–Romance evidence for refining our understanding of the nature of contact‐induced change and how, when modelled in terms of parameter hierarchies, exogenous change can be formally distinguished from endogenous change. In particular, it is proposed that a formal hallmark of contact‐induced change is the so‐called Catapult Effect, the force of which is also able to capture how some well‐known effects of exogenous change such as acceleration, convergence and hybridism—terms frequently employed in the literature with very loose and often different meanings—can be successfully formalised by way of parameter hierarchies. The article concludes with a reassessment of a significant aspect of the ‘multiple causation’ hypothesis regarding exogenous change, namely, the role of layering in contact. It is proposed that certain developments are best analysed as the output of a layering of successive changes, noting how the endogenous vs exogenous nature of the input change in the first layer is not trivial but accounts for the presence of what is termed the ‘Instability Effect’.