How individuals change language

TL;DR

This paper introduces a comprehensive mathematical model to understand how individual linguistic innovations lead to language change at the population level, emphasizing the role of lifelong incremental change and social networks.

Contribution

It presents a general model that predicts population language change from individual behaviors and compares these predictions with historical data.

Findings

Errors in childhood language acquisition are weakly supported as a primary cause.

Incremental changes across the lifespan are more consistent with observed data.

Social network effects significantly influence language change dynamics.

Abstract

Languages emerge and change over time at the population level though interactions between individual speakers. It is, however, hard to directly observe how a single speaker's linguistic innovation precipitates a population-wide change in the language, and many theoretical proposals exist. We introduce a very general mathematical model that encompasses a wide variety of individual-level linguistic behaviours and provides statistical predictions for the population-level changes that result from them. This model allows us to compare the likelihood of empirically-attested changes in definite and indefinite articles in multiple languages under different assumptions on the way in which individuals learn and use language. We find that accounts of language change that appeal primarily to errors in childhood language acquisition are very weakly supported by the historical data, whereas those that allow speakers to change incrementally across the lifespan are more plausible, particularly when combined with social network effects.