Many rule-based models of phonology such as Chomsky and Halle (1968) posit that phonological grammars consist of ordered sets of rules. Opaque interactions result when a rule applies despite its environment not being met on the surface or a rule failing to apply despite its environment being met on the surface. This class introduces/reviews rule-based models, examines what it means for an analysis to be opaque, and surveys examples.

Level: Introductory/intermediate