In this article, I analyse the word-prosodic system of Drubea and Numèè, two of the rare tonal Oceanic languages. Building on Rivierre’s (1973) seminal work, I show that the word-prosodic system of these two languages can be analysed as involving only register features: an underlying downstep and a postlexical epenthetic upstep. Drubea and Numèè are thus tonal languages without tones stricto sensu. This new type of word-prosodic system has both theoretical and typological implications: (i) register features, defined as in Snider’s (1999) Register Tier Theory, need not be subordinate to or associated with tones, and may exist in the absence of tone, including in underlying representation; (ii) tonal systems come in two types: tone-based systems in which the tonal contrasts are defined paradigmatically, as in most tone languages, and register-based systems where tonal contrasts are defined syntagmatically, as in Drubea and Numèè.

This article examines a case of phonological opacity in Uyghur resulting from an interaction between backness harmony and a vowel reduction process that converts harmonic vowels into transparent vowels. A large-scale corpus study shows that although opaque harmony with the underlying form of a reduced vowel is the dominant pattern, cases of surface-apparent harmony also occur. The rate of surface-apparent harmony varies across roots and is correlated with a number of factors, including root frequency. These data pose problems for standard accounts of opacity, which do not predict such variation. I propose an analysis where variation emerges from conflict between a paradigm uniformity constraint mandating that the harmonising behaviour of a root remains consistent, and surface phonotactic constraints. This is implemented in a parallel model by scaling constraint violations according to certainty in a root’s harmonic class. This aligns with past work suggesting some opacity is driven by paradigm uniformity.