Quantifying Word Order Freedom in Dependency Corpora

Using recently available dependency corpora, we present novel measures of a key quantitative property of language, word order freedom: the extent to which word order in a sentence is free to vary while conveying the same meaning. We discuss two topics. First, we discuss linguistic and statistical issues associated with our measures and with the annotation styles of available corpora. We find that we can measure reliable upper bounds on word order freedom in head direction and the ordering of certain sisters, but that more general measures of word order freedom are not currently feasible. Second, we present results of our measures in 34 languages and demonstrate a correlation between quantitative word order freedom of subjects and objects and the presence of nominative-accusative case marking. To our knowledge this is the first large-scale quantitative test of the hypothesis that languages with more word order freedom have more case marking (Sapir, 1921; Kiparsky, 1997).