From discourse to syntax and back: The lifecycle of Kuuk Thaayorre ergative morphology

The ergative inflection of Kuuk Thaayorre nouns is remarkably irregular. More than 15 distinct ergative forms are attested, none of which is phonologically predictable. This ergative inflection is also remarkable for its optional use. In spite of its primarily syntactic function, it may also be used to mark pragmatically ‘unexpected’ intransitive subjects, or be omitted where the referent of a transitive subject is easily retrieved from the discourse context or world knowledge. This article proposes that both the formal irregularity of the Kuuk Thaayorre ergative morpheme and its optionality have their origins in a language-wide historical process of phonological erosion. The suite of diachronic processes this erosion triggered a bidirectional grammaticalisation pathway, whereby grammatical (ergative) morphs were imbued with pragmatic functions even as originally pragmatic (focal) morphs were reanalysed as grammatical.