Grammatical cues to subjecthood are redundant in a majority of simple clauses across languages

TL;DR

This study investigates how often grammatical cues like word order are redundant with meaning across languages, showing that while often unnecessary, they are crucial for conveying specific, non-inferable information in natural language.

Contribution

It combines behavioral experiments and cross-linguistic computational analysis to quantify redundancy of grammatical cues in multiple languages, revealing their importance in language comprehension.

Findings

High accuracy in human subject identification (~87-89%) across languages.

Neural network classifiers perform similarly across 30 languages, indicating consistent redundancy.

Grammatical cues are crucial for conveying roles in non-prototypical and reversible scenarios.

Abstract

Grammatical cues are sometimes redundant with word meanings in natural language. For instance, English word order rules constrain the word order of a sentence like "The dog chewed the bone" even though the status of "dog" as subject and "bone" as object can be inferred from world knowledge and plausibility. Quantifying how often this redundancy occurs, and how the level of redundancy varies across typologically diverse languages, can shed light on the function and evolution of grammar. To that end, we performed a behavioral experiment in English and Russian and a cross-linguistic computational analysis measuring the redundancy of grammatical cues in transitive clauses extracted from corpus text. English and Russian speakers (n=484) were presented with subjects, verbs, and objects (in random order and with morphological markings removed) extracted from naturally occurring sentences and were asked to identify which noun is the subject of the action. Accuracy was high in both languages (~89% in English, ~87% in Russian). Next, we trained a neural network machine classifier on a similar task: predicting which nominal in a subject-verb-object triad is the subject. Across 30 languages from eight language families, performance was consistently high: a median accuracy of 87%, comparable to the accuracy observed in the human experiments. The conclusion is that grammatical cues such as word order are necessary to convey subjecthood and objecthood in a minority of naturally occurring transitive clauses; nevertheless, they can (a) provide an important source of redundancy and (b) are crucial for conveying intended meaning that cannot be inferred from the words alone, including descriptions of human interactions, where roles are often reversible (e.g., Ray helped Lu/Lu helped Ray), and expressing non-prototypical meanings (e.g., "The bone chewed the dog.").