This article analyzes the process that I call Liquid Lowering which turns high vowels $i$ and ɨ  into $e$ before liquids, schematically iɨ → e/ – rl. The process began to operate in Polish in the 16th century. I look at the modern reflexes of Liquid Lowering in Standard Polish and in Kurpian, a dialect of Polish that dates back to the 17th century, and argue that the rule is dead in Standard Polish but not in Kurpian, where it is productive in derived environments. The modeling of Liquid Lowering as a phonological process has implications for phonological theory. In particular, it calls for the recognition of derivational levels, as envisaged by Derivational Optimality Theory. It is argued that Standard Optimality Theory, with its principle of strict parallelism, cannot account for the data because it runs into insoluble ranking paradoxes. Furthermore, the analysis bears on the issue of abstractness by positing vowels that never occur phonetically. The abstract vowels are exchanged for the actually occurring vowels before reaching the surface representation. I term this type of shift change virement.