Different phenomena are known to exhibit sensitivity to the person/animacy (P/A) features of clausal arguments. One example is P/A-based split ergativity; another is P/A-conditioned auxiliary selection (e.g., in Italo-Romance; D'Alessandro & Roberts 2010). Building on Coon's (2010) account of aspect-based split ergativity, we argue that P/A-based split ergativity arises when structural factors conspire to place the subject and object in separate case/agreement domains, and that the same structural factors inhibit the head-incorporation which underlies the have/be alternation (Freeze 1992, Kayne 1993). We thus offer a unified account of aspect-based and P/A-based split ergativity, which also extends to person-conditioned auxiliary selection.