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

Grammatical Change Begins within the Word: Causal Modeling of the Co-evolution of Icelandic Morphology and Syntax Fermin Moscoso del Prado Martin (fmoscoso@linguistics.ucsb.edu) Department of Linguistics, UC – Santa Barbara Santa Barbara, CA 93106 USA Abstract 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. Keywords: Granger-causality; Historical Linguistics; Icelandic; Information Theory; Morphological paradigms; Syntactic complexity. Introduction A common observation in the field of Historical Linguistics is that grammatical changes in language tend to be cascaded (e.g., Biberauer & Roberts, 2008; Lightfoot, 2002). Changes at a given level of language (e.g., phonology, morphology, syntax, …) disturb the unstable equilibrium at which human languages reside, triggering a cascade of further linguistic changes as a result. These cascaded changes continue until the system reaches a new meta-stable state (e.g, Croft, 1995; Smith, 1996). For instance, it is widely documented that the loss of the grammatical case markers (morphology) in Late Middle English led to a more rigid word order (syntax) in Early Modern English (cf., Fisiak, 1984). Traditionally, historical linguists have tracked these cascaded changes by looking for the earliest document at which a particular grammatical innovation can be found or – conversely– at the latest time in which a later extinct construction was documented. Historical linguistics often relies on hard dichotomies on the presence or absence of individual words, affixes, or constructions. This approach is clearly useful for documenting the approximate time at which particular constructions appeared or disappeared. The approach is however limited in its power to detect more subtle forms of grammatical change. For instance, as I will argue in this study, Icelandic morphological paradigms are remarkably resilient, having survived with little change for a such a long period, that most of its current system can be directly traced –virtually unchanged– all the way up to the Old West Norse of the XII century. However, despite the striking conservativeness of the Icelandic paradigms, their patterns of usage have changed along this period. One can obtain a higher degree of sensitivity by studying the frequencies (and implicitly the probabilities) of usage of different constructions in diachronic scale. These often reveal gradual changes in the grammar of a language. For instance, Ellegard (1953) documented how the usage of the English periphrastic do construction (e.g., I do not speak vs. I speak not, or Do you speak? vs. Speak you? ) arose gradually –rather than abruptly– during a period of two hundred years, from the late XV century to early XVIII century. With the wide availability of diachronic corpora in electronic form, these frequency-based methods have gained much prominence in recent years (see Hilpert & Gries, in press, for a recent survey of quantitative methods in historical linguistics). Admittedly, frequency methods offer an improved sensitivity to the gradualness of grammatical changes along time. Most often, these methods are applied to relate the evolution of the usage of a particular construction in different contexts. The natural tools to achieve this type of inferences are different types of regression analysis. These analyses study the correlations between different factors that might affect the emergence or demise of a construction. For instance, Hilpert (2013) uses such tools to analyze the evolution of (among many others) the patterns of usage of the English future constructions will vs. be going to. Using a logistic regression analysis, he identifies several factors that significantly co-occur with the uses of either construction. One must –however– keep in mind the old adagio: “correlation does not imply causation”. Even in the cases when one finds significant correlation between the frequencies of use and co-occurrence of different linguistic patterns and constructions, it still remains problematic to argue that one pattern causes another. Back to example above, the causal connection between the loss of grammatical case and the fixation of word order is in fact not so trivial on the basis of the historical data alone. Evidently, I cannot infer that I have just had dinner because it stopped raining, even if I observed both events in a sequence. To make such arguments, I would require some form of statistical evidence on how reliably do I start eating whenever it stops raining. Similarly, just the temporal sequentiality between the loss of case marking and the emergence of rigid word order does not –by itself alone– necessarily warrant causality. For instance, Kiparsky (1996) discusses how fixed word order arose also in Icelandic while the case markers were preserved.