Elizabeth Pearce
The verb paradigms of declarative clauses in Unua (an Oceanic language of Malakula, Vanuatu) have a distinct Irrealis prefix b- contrasting with zero marking for the Realis. In relative clauses, however, the Irrealis b- contrasts with a prefix m- encoding realis interpretations. On the basis of comparative evidence, the synchronic m- prefix is a remnant of an earlier Realis *mw- that has become specialized for use in relative clauses. The diachronic loss of overt morphology in unmarked categories is not unusual. What is unusual in the Unua case is the retention and specialization of the morphology for the unmarked category in a sub-class of constructions, relative clauses. This paper sketches out the likely significant factors in the historical changes giving rise to the synchronic state. These include conditioned phonological weakening and effects of the salience of the m- prefix in the cross-construction noun modification functional role.