peer reviewed ; robustness in language processing and learning (MacWhinney et al. 2014), both from a typological and diachronic perspective. Specifically, we assess the potential benefits or costs of redundancy in morphosyntactic marking of participant roles, comparing and testing two opposing hypotheses: On the one hand, following the most crucial tenet in usage-based linguistics that language use affects – or even determines – grammar (Bybee 2010), we assume that language is organised in a way that facilitates efficient usage (e.g. Gibson et al. 2019). On this account, redundant marking should be dispreferred. Well-known typological ‘trade-off’ distributions and diachronic trajectories between word order and morphological case marking seem to support this point (Fedzechkina et al. 2017). Furthermore, prepositional marking is often only applied in contexts where it comes with some added processing benefit (cf. Pijpops et al. 2018 on the impact of complexity on Dutch transitive object marking, or Tal et al. 2020, Levshina 2021 on ambiguity/atypicality in differential object marking). On the other hand, however, we pursue Van de Velde's (2014) argument that a certain amount of redundancy – or rather, ‘degenerate’ marking (involving many-to-many relationships) – is in fact beneficial from a usage perspective: redundancy constitutes an indispensable component of any degenerative Complex Adaptive System, and thus also of language (Steels 2000; Beckner et al. 2009). Such redundancy/degeneracy comes with two important advantages, viz. robustness and evolvability: most importantly for the present paper, the former entails that redundant marking offers protection against information loss in the noisy language channel, even though it may be less efficient. Redundancy is furthermore assumed to increase learnability, particularly in more complex situations (e.g. Tal et al. 2021). Our case study to assess the plausibility of what we call the ‘strict-efficiency’ versus the ‘robustness’ account is participant role marking in ...