TAM splits in conditional argument indexing

A common type of split ergativity is conditioned by tense and/or aspect in that an ergative-absolutive system occurs in the past tense or perfective aspect and a nominative-accusative system occurs in the non-past tense(s) or imperfective aspect (DeLancey 1982, Payne 2006). This finding, however, pertains to case marking only. Using a genetically diverse typological sample on conditional argument indexing in 83 languages (Walker 2024, Walker & Van Lier under review), the present study explores if a similar tendency can be found for indexing. Within the database, 22 languages display indexing conditioned by TAM (tense, aspect, mood) factors. Across 17 languages, a clear trend regarding aspect and indexing was found: imperfective, progressive, and non-completive aspect condition a nominative-accusative system while perfective, terminative, and completive aspect condition an ergative-absolutive system. For tense and mood, however, no such clear relationship was found. For the remaining 5 languages, the TAM split applied to a specific person/number value only. We conclude that for aspect, but not for tense and mood, our findings correspond with previous literature on split-ergativity in case marking.