Middle Welsh is a language with a restricted set of morphosyntactic distinctions for grammatical relations and with relatively free word order in positive main declarative causes. However, syntactic ambiguity rarely, if ever, arises in natural texts. The present article shows in a corpus-based study how syntactic ambiguity is prevented and how morphological features interact with two referential properties, namely animacy and accessibility, in order to successfully identify grammatical relations in Middle Welsh. Further lower-tier factors are the semantics of the verb and the wider narrative context. The article complements recent insights suggesting that subject-verb agreement is not only determined by wordorder patterns, but also by referential properties of subjects.