Assessing the pace of language change via estimated loan word volumes: Implications for Irish

Assessing the pace of language change in historical settings can be impeded by a lack of contemporary documents. Loan word adaptation can provide an additional window on this problem. Given a series of formerly productive phonological processes and a well studied donor language, a search algorithm equipped with a simple phonotactic probability model can estimate how many loans entered before each phonological period ended. The population of loans during a period is a plausible proxy for the duration of the period, so periods with few loans could have been subject to rapid change. Our approach is illustrated with the Latin loans in Irish, shedding light on a period that pre-dates substantial written records. This period includes the development of rhythmic syncope in Irish, a process that has garnered interest due to its resistance to analysis in parallel but not serial models of phonology (McCarthy 2008, inter alia). Strikingly, our model finds that few loans entered during the rhythmic syncope phase of Irish, which is consistent with the process quickly becoming unproductive, as has been found for other languages (Bowers 2019, inter alia).