Lexicon against naturalness: Unnatural gradient phonotactic restrictions in Tarma Quechua

It has been shown in separate studies that phonological grammar can operate probabilistically and in phonetically unnatural directions. This paper documents a case in which both of these properties of phonological grammar are true at the same time. We create a new corpus of Tarma Quechua vocabulary (based both on published and unpublished data), and argue that the unnatural probabilistic phonotactic trends in the Tarma Quechua lexicon are statistically significant and show some signs of productivity based on morphophonological alternations. We also perform an acoustic analysis of existing recordings to support the phonetic status of the unnatural gradient restriction. To our knowledge, this is the first report of a fully unnatural gradient phonotactic restriction on segmental structure. The existence of unnatural probabilistic phonology has broad theoretical consequences because it requires probabilistic approaches to phonology to derive unnatural patterns. While weighted-constraint approaches are more powerful than nonprobabilistic approaches, we argue that models without unnatural constraints are not sufficient for deriving the Tarma Quechua data. We adopt a framework for evaluating phonological analyses using the goodness of fit measurement. This quantitative evaluation approach supports analyses with some, but not all, of the relevant conceivable unnatural constraints. We argue that the proposed approach can serve to evaluate other models and approaches.