A stronger null hypothesis for crossing dependencies

TL;DR

This paper introduces a new null hypothesis for the number of crossing dependencies in syntactic trees, accounting for edge lengths, which better explains the natural non-crossing structure of sentences without assuming minimization principles.

Contribution

It proposes a novel null hypothesis that predicts crossing dependencies considering edge lengths, challenging the need for crossing minimization principles in syntax.

Findings

Null hypothesis accurately predicts crossing dependencies with small error.

Crossing minimization is not necessary to explain non-crossing dependencies.

New model advances understanding of syntactic structure formation.

Abstract

The syntactic structure of a sentence can be modeled as a tree where vertices are words and edges indicate syntactic dependencies between words. It is well-known that those edges normally do not cross when drawn over the sentence. Here a new null hypothesis for the number of edge crossings of a sentence is presented. That null hypothesis takes into account the length of the pair of edges that may cross and predicts the relative number of crossings in random trees with a small error, suggesting that a ban of crossings or a principle of minimization of crossings are not needed in general to explain the origins of non-crossing dependencies. Our work paves the way for more powerful null hypotheses to investigate the origins of non-crossing dependencies in nature.