|Abstract:||This paper analyzes the vocative truncation pattern in Korean from the viewpoint of Message-Oriented Phonology (MOP: Hall et al. 2016), which capitalizes on the idea that sound patterns are governed by a principle that makes message transfer effective. In the traditional naming pattern, Korean first names consist of a generation marker and a unique portion, and the order between these two elements alternates between generations. To derive vocative forms, the generation marker is truncated, and the suffixal [(j)a] is attached to the unique portion. We argue that MOP naturally predicts this type of truncation. As the generation marker is shared by all the members of the same generation, the generation marker is highly predictable and hence does not reduce uncertainty about the intended message. To achieve effective communication, predictable portions are deleted. To the extent that our analysis is on the right track, it implies that MOP is relevant not only to phonetic implementation patterns, but also to (morpho-)phonological patterns. It also provides support to MOP based on data from a non-Indo-European language. Finally, we aim to integrate insights of MOP with a more formal proposal like Optimality Theory (Prince and Smolensky 1993/2004), by relating the predictability of a contrast to the ranking of the faithfulness constraint that it protects, following the spirit of the P-map hypothesis (Steriade 2001/2008).