Liquid polarity, positional contrast, and diachronic change : clear and dark /r/ in Latin

Apparently disparate sound changes in Latin, involving both vowels and consonants but sensitive to /r/, can be explained by reconstructing a positional clear/dark contrast in /r/, motivated by the seldom-mentioned “liquid polarity” effect. Examining these diachronic processes together allows us to see a larger picture, providing evidence for the reconstruction of successive past synchronic states. Latin /r/ mirrored the behaviour of Latin /l/ up to the first century BC: /l/ was dark and /r/ was clear in codas, and /r/ was dark and /l/ was underspecified for tongue body position in onsets. Darkness in /r/ was partly implemented through the selection of r-type: dark onset approximant and clear coda tap. Later, coda /r/ became an approximant like onset /r/, and subsequently both became trills, resulting in the erosion of the positional contrast and the liquid polarity effect.