Bringing agents into focus: Competing motivations in differential agent marking

This paper presents the first corpus-based study of the factors underlying the presence vs. absence of case-marking on transitive agents in a fluid differential agent marking (“optional ergative”) language which includes a quantitative account of the role of information structure, alongside other factors. The language under investigation is Jaminjung/Ngaliwurru (J/Ng), a Mirndi language of Northern Australia. 502 clauses with overt agents were extracted from a total of 112 audio-linked texts (ca. 13,000 intonation units) representing 20 speakers. The clauses were coded for pronominal vs. lexical status of the agent noun phrase, definiteness, person and animacy of agent, TAM, and verb class – factors which have been reported to affect the use of agent marking in other languages (see McGregor & Verstraete 2010 for an overview). In addition, in view of mounting cross-linguistic evidence for an influence of information structure on differential agent marking, the information structure category (topic and focus) of the agent NP was coded, based on independent prosodic and contextual criteria. A generalised linear mixed model (GLMM) with logistic link function and MuMIN (Bartoń, 2015; Marschner, 2011) was applied to the 502 tokens to determine the factors affecting the use of agent marking. The analysis shows that agent marking occurs 76% (n=382) of the time, but is more likely if the agent is third person (83%, p<0.001), under focus (84%, p<0.001), and the verb is non-effective (81%, p<0.001). The model explains a good amount of variation in the data set (conditional R2=0.51). The first two of these tendencies, although independent of and potentially competing with one another, can be regarded as manifestations of an overarching principle of Economy (e.g. Silverstein 1976; McGregor 1992; Aissen 1999; Malchukov 2008, 2015): since overt topics are expected to be agents rather than patients, and 1st and 2nd pronouns are more likely to be agents than patients, the marking of their role can be omitted. The higher frequency of topical agents and speech act participant pronouns as agents as opposed to patients is indeed confirmed within the J/Ng corpus. As predicted by Malchukov (2008, 2015), overt ergativity can however also be subject to a functional constraint which is orthogonal to Economy, labelled “Indexing”. This manifests itself in the tendency for less prototypical agents to not be marked as agents, e.g. in events of a low degree of impact on the second participant (cf. also Tsunoda 1981). The third factor identified for J/Ng – a statistically significant tendency for the agents of verbs of transitive possession and speech verbs to be unmarked – directly reflects this constraint. In sum, differential agent marking in J/Ng presents yet another instance of “soft constraints mirroring hard constraints” (Bresnan et al. 2001), in that the statistical tendencies identified for J/Ng mirror some of the factors identified as underlying strict ergative splits cross-linguistically. Crucially, in addition, our findings underline the importance of information structure for differential case marking. Moreover, the findings shed doubt on the usefulness of a generalised notion of “argument strength” (e.g. De Hoop 1999; De Hoop & Narasimhan, 2005), and on arguments against functional constraints on split case systems which are based on the assumption of a single prominence scale encompassing information structure, person and animacy (Bickel et al. 2015). 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