This work explores the coupling of person-split nominative objects with anomalous subjects, or Jahnsson's Rule. In Breton, split-nominative objects spread from an Icelandic-like combination with oblique subjects of unaccusatives, to Finnish-like ones with subjects of transitives in constructions like the imperative, and then retreated piecewise. The developments admit of motivations external to (I-)language, such as frequency entrenchment [Haspelmath 2004], but are bounded by the coupling of Jahnsson's Rule, and disfavour external sources for it like ambiguity avoidance [Dixon 1994]. An approach is explored through constraints on φdependencies, their relationship to case and licensing, and their interaction with grammaticalisable partial φ-specification, building on work on the Person-Case Constraint [Anagnostopoulou 2003]. The anomalies of the restricting subject are analysed as person-only specification, and extended from obliques to pronouns minimal in absence number + n/N, such as imperative pro [Zanuttini et al. 2013] and human impersonals [Malamud 2012]. The effect on the split-nominative in ineffability or accusative of the restricted persons is analysed through the integration of dependent case into Φ/Case theory [Kalin 2018] but the developments under study lead to recasting of apparent syntactic variation through externalisability [Coon and Keine 2020].Read less <