Probing the vertical and horizontal signal of parametric syntax

In this paper we argue that the Parametric Comparison Method (PCM, Longobardi and Guardiano 2009), thanks to its capability of combining insights from formal grammar, historical/comparative linguistics, quantitative sociolinguistics (dialectometry), and computer-assisted techniques, can be successfully implemented as a powerful device to capture, distinguish and precisely assess the effect of vertical and contact-induced change in (closely) related systems. In particular, we show that with the aid of a strongly constrained theory of syntactic variation and change we become able to identify the significant diachronic signal retained by dialect syntax even in contexts of massive horizontal transmission and, at the same time, to identify paths of spread of syntactic characters.