Grammatical Change Begins within the Word: Causal Modeling of the Co-evolution of Icelandic Morphology and Syntax

I introduce a combination of information-theoretical and causal modeling to study the cascading of changes between the morphology and the syntax of a language on a diachronic scale. Through the analysis of a historical treebank of Icelandic language ranging from the XII to the XXI century, I show that it is changes in the inflectional morphology of the language that triggered changes in its syntax. This offers a novel and powerful approach to draw conclusions in historical linguistics from a macroscopic perspective. In addition, these findings have implications for the dynamical properties of the linguistic system.