This paper addresses one of the most contested issues in phonology: unnatural alternations. First, non-natural phonological processes are subdivided into unmotivated and unnatural. The central topic of the paper is an unnatural process: post-nasal devoicing (PND). I collect thirteen cases of PND and argue that in all reported cases, PND does not derive from a single unnatural sound change (as claimed in some individual accounts of the data), but rather from a combination of three sound changes, each of which is phonetically motivated. I present new evidence showing that the three stages are directly historically attested in the pre-history of Yaghnobi. Based on several discussed cases, I propose a new diachronic model for explaining unnatural phenomena called the Blurring Process and point to its advantages over competing approaches (hypercorrection, perceptual enhancement, and phonetic motivation). The Blurring Process establishes general diachronic conditions for unnatural synchronic processes and can be employed to explain unnatural processes beyond PND. Additionally, I provide a proof establishing the minimal sound changes required for an unmotivated/unnatural alternation to arise. The Blurring Process and Minimal Sound Change Requirement have implications for models of typology within the Channel Bias approach. This paper thus presents a first step toward the ultimate goal of quantifying the influences of Channel Bias on phonological typology.
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