|Abstract:||Two strategies of case marking in natural languages are discussed. These are defined as two violable constraints whose effects are shown to converge in the case of differential object marking but diverge in the case of differential subject marking. The strength of the case bearing arguments will be shown to be of utmost importance for case marking as well as voice alternations. The strength of arguments can be viewed as a function of their discourse prominence. The analysis of the case marking patterns we find cross-linguistically is couched in a bidirectional OT analysis.