Diachronic pathways to case marking alignment and what they mean for the explanation of synchronic cross-linguistic patterns

Case marking alignment has been assumed to reflect principles of optimization: dedicated case marking is limited to arguments more in need of disambiguation, and semantically or pragmatically similar arguments are encoded by the same case forms. This view is based on the synchronic properties of the relevant alignment patterns and the cross-linguistic rarity of other logically possible ones, not diachronic phenomena involved in their emergence or cross-linguistic distribution. This paper explores several developmental processes that recurrently give rise to accusative, ergative, and active case marking alignment cross-linguistically, including reanalysis of argument structure, the development of case forms through grammaticalization or phonological reduction, and the extension of an existing case form to novel contexts. These processes appear to be driven by inherent or contextual properties of particular source constructions, independent of principles of optimization in the use of case marking. The synchronic properties of the resulting alignment patterns cannot be taken as evidence for such principles either, because they are due to inheritance (a case form inherits the distribution of particular source elements or developmental processes, which is unrelated to the assumed optimization principles) or residue (a case form becomes restricted to particular arguments as a new form develops for the other arguments, also independently of these principles). These facts call for a source-oriented approach to case marking alignment and recurrent cross-linguistic patterns in general, one where the focus shifts from the synchronic properties of individual patterns to unraveling the effects of several different diachronic phenomena that give rise to individual patterns and shape their cross-linguistic distribution over time.