Nominal case marking has reached a high degree of syncretism in Middle Welsh, and nominal forms are distinguished only for singular and plural. Additionally, Middle Welsh does not possess relative pronouns which can morphologically or syntactically signal an antecedent's precise syntactic function within a relative clause. This means that in certain constructions morpho-syntactic cues may not always be sufficient to define syntactic relations in Middle Welsh relative clauses. The following study is based on the Four Branches of the Mabinogi and selections from Middle Welsh historiographical texts. It uses a statistical approach to evaluate the frequencies with which ambiguous syntactic relations appear in Middle Welsh relative clauses, and assesses the contribution of other concepts like accessibility, animacy, co-text and general knowledge of the world available within a clause for the assignment of syntactic relations.