The natural stability of autonomous morphology

TL;DR

This paper explains the natural stability of autonomous morphology in language through computational models showing how rational inference and dissociative evidence prevent collapse of morphological classes over time.

Contribution

It introduces a novel diachronic dynamic model based on attraction and repulsion between categories driven by dissociative evidence, explaining morphological resilience.

Findings

Dissociative evidence creates a repulsion dynamic among morphomic classes.

Conditional entropy has limitations as a predictability measure during change.

Autonomous morphology emerges naturally from rational inference processes.

Abstract

Autonomous morphology, such as inflection class systems and paradigmatic distribution patterns, is widespread and diachronically resilient in natural language. Why this should be so has remained unclear given that autonomous morphology imposes learning costs, offers no clear benefit relative to its absence and could easily be removed by the analogical forces which are constantly reshaping it. Here we propose an explanation for the resilience of autonomous morphology, in terms of a diachronic dynamic of attraction and repulsion between morphomic categories, which emerges spontaneously from a simple paradigm cell filling process. Employing computational evolutionary models, our key innovation is to bring to light the role of `dissociative evidence', i.e., evidence for inflectional distinctiveness which a rational reasoner will have access to during analogical inference. Dissociative evidence creates a repulsion dynamic which prevents morphomic classes from collapsing together entirely, i.e., undergoing complete levelling. As we probe alternative models, we reveal the limits of conditional entropy as a measure for predictability in systems that are undergoing change. Finally, we demonstrate that autonomous morphology, far from being `unnatural' (e.g. \citealt{Aronoff1994}), is rather the natural (emergent) consequence of a natural (rational) process of inference applied to inflectional systems.