Learning and emergent properties of inflection class systems

Andrea Sims (Ohio State University)
Learning and emergent properties of inflection class systems

Theoretical morphologists and typologists have long appealed to learnability to explain emergent properties of the world’s languages. The high-level argument is simple: All natural languages must be learned and unlearnable linguistic systems cannot survive. Therefore, the learning mechanism provides constraints on what sorts of languages can exist in the world. However, when we examine the argument in detail it does not prove simple to define learnability and different theories offer different ideas of what the morphological knowledge to be acquired is. I examine these issues via two examples of emergent inflectional structure: irregularity and defectiveness. Theories commonly treat irregularity and defectiveness as falling outside of morphological knowledge; in turn this shapes claims about the kinds of patterns that are learnable. I argue instead that at least some examples of irregularity and defectiveness are interact with other elements in their inflectional systems in fundamental ways, motivating a systems-oriented approach to the phenomena. I use an iterated learning model to examine the nature of these systemic interactions, how irregularity and defectiveness emerge and persist in inflectional systems, and what this can tell us about the role of learnability as explanation.