A Stochastic Model of Language Change through Social Structure and Prediction-driven Instability

Language change is paradoxical: Children acquire their native language accurately, yet over time, the language can change. Some changes may be attributed to an external event, such as political upheaval, but not every instance of language change seems to have an external cause. A possible resolution to this paradox comes from the facts that (1) spoken language has inherent variation and (2) children may take social structure into account, giving more or less weight to speech patterns correlated with age and social status. Individuals vary in how they use their native language, and chance local fluctuations in such variation might be enough to trigger a language change. As we will see in Section 3, a mean-field model in which children learn from the entire population equally does not lead to spontaneous change, even in the presence of random variation. However, in Section 4 we will discuss a simple modification of the model, in which children can detect age-correlated patterns in variation. When subject to random fluctuations, this model does exhibit spontaneous language change: Children can detect accidental correlations between age and speech, predict that the population is about to undergo a language change, and accelerate the change, a process I will call prediction-driven instability.