Numeral classifiers and number marking in Indo-Iranian

This paper investigates the origins of sortal numeral classifiers in the Indo-Iranian languages. While these are often assumed to result from contact with non-Indo-European languages, an alternative possibility is that classifiers developed as a response to the rise of optional plural marking. This alternative is in line with the so-called Greenberg-Sanches-Slobin (henceforth GSS) generalization. The GSS generalization holds that the presence of sortal numeral classifiers across languages is negatively correlated with obligatory plural marking on nouns. We assess the extent to which Indo-Iranian classifier development is influenced by loosening of restrictions on plural marking using a sample of 65 languages and a Bayesian phylogenetic model, inferring posterior distributions over evolutionary transition rates between typological states and using these rates to reconstruct the history of classifiers and number marking throughout Indo-Iranian, constrained by historically attested states. We find broad support for a diachronically oriented construal of the GSS generalization, but find no evidence for a strong bias against the synchronic co-occurrence of classifiers and obligatory plural marking. Inspection of the most likely diachronic trajectories in individual lineages in the tree shows a stronger effect of the GSS among Iranian languages than Indo-Aryan languages. Taken as a whole, these findings suggest that the association of classifiers and optional number marking in Indo-Iranian is neither solely the effect of universal mechanisms nor of the contingency of local contact histories.