Non-crossing dependencies: least effort, not grammar

TL;DR

This paper challenges the null hypothesis that low frequency of syntactic dependency crossings is due to arbitrary word order, proposing instead that dependency length reduction explains crossing avoidance in language.

Contribution

It introduces null hypotheses based on dependency lengths, arguing that crossing minimization results from resource constraints rather than grammatical rules.

Findings

Crossings decrease with shorter dependencies.

Star dependency structures are unrealistic for natural language.

Dependency length reduction explains crossing avoidance better than grammatical constraints.

Abstract

The use of null hypotheses (in a statistical sense) is common in hard sciences but not in theoretical linguistics. Here the null hypothesis that the low frequency of syntactic dependency crossings is expected by an arbitrary ordering of words is rejected. It is shown that this would require star dependency structures, which are both unrealistic and too restrictive. The hypothesis of the limited resources of the human brain is revisited. Stronger null hypotheses taking into account actual dependency lengths for the likelihood of crossings are presented. Those hypotheses suggests that crossings are likely to reduce when dependencies are shortened. A hypothesis based on pressure to reduce dependency lengths is more parsimonious than a principle of minimization of crossings or a grammatical ban that is totally dissociated from the general and non-linguistic principle of economy.