Some languages constrain the recursive embedding of NPs to some specific morphosyntactic types, allowing it, for example, only with genitives but not with bare juxtaposition. In Indo-European, every type of NP embedding-genitives, adjectivizers, adpositions, head marking, or juxtaposition-is unavailable for syntactic recursion in at least one attested language. In addition, attested pathways of change show that NP types that allow recursion can emerge and disappear in less than 1,000 years. This wide-ranging synchronic diversity and its high diachronic dynamics raise the possibility that at many hypothetical times in the history of the family recursive NP embedding could have been lost for all types simultaneously, parallel to what has occasionally been observed elsewhere (Everett 2005, Evans & Levinson 2009). Performing Bayesian phylogenetic analyses on a sample of fifty-five languages from all branches of Indo-European, we show, however, that it is extremely unlikely for such a complete loss to ever have occurred. When one or more morphosyntactic types become unavailable for syntactic recursion in an NP, an unconstrained alternative type is very likely to develop in the same language. This suggests that, while diachronic pathways away from NP recursion clearly exist, there is a tendency-perhaps a universal one-to maintain or develop syntactic recursion in NPs. A likely explanation for this evolutionary bias is that recursively embedded phrases are not just an option that languages have (Fitch et al. 2005), but they are in fact preferred by our processing system.*

The use of interrogative pronouns as relative clause markers is often mentioned as a typical feature of European languages. This study presents an empirical approach to the distribution of interrogative pronouns as relative clause markers in time and space in the Indo-European language family. Based on a comprehensive sample of ancient and modern Indo-European languages, it is shown that interrogative-marked relative clauses are present in all stages of Indo-European within and outside of Europe. An analysis by branch suggests that this constitutes a case of parallel innovations subsequently spreading via language contact. The study also shows that interrogatives are used as relative clause markers independently of whether they are inflected pronouns or invariable markers.

We provide a discussion of some of the challenges in using statistical methods to investigate the morphology-syntax distinction cross-linguistically. The paper is structured around three problems related to the morphology-syntax distinction: (i) the boundary strength problem; (ii) the composition problem; (iii) the architectural problem. The boundary strength problem refers to the possibility that languages vary in terms of how distinct morphology and syntax are or the degree to which morphology is autonomous. The composition problem refers to the possibility that languages vary in terms of how they distinguish morphology and syntax: what types of properties distinguish the two systems. The architecture problem refers to the possibility that languages vary in terms of whether a global distinction between morphology and syntax is motivated at all and the possibility that languages might partition phenomena in different ways. This paper is concerned with providing an overarching review of the methodological problems involved in addressing these three issues. We illustrate the problems using three statistical methods: correlation matrices, random forests with different choices for the dependent variable, and hierarchical clustering with validation techniques.

Subgrouping language varieties within dialect continua poses challenges for the application of the comparative method of historical linguistics, and similar claims have been made for the use of Bayesian phylogenetic methods. In this article, we present the first Bayesian phylogenetic analysis of the Mixtecan language family of southern Mexico and show that the method produces valuable results and new insights with respect to subgrouping beyond what the comparative method and dialect geography have provided. Our findings reveal potential new subgroups that should be further investigated. We show that some unexpected groupings raise important questions for phylogenetics and historical linguistics about the effects of different methods of primary data gathering and organization that should be considered when interpreting subgrouping results.