This paper shows that Basaá (A.43) possesses two relative clause strategies, one involving a gap and another a relative pronoun. The distribution of these two strategies follows the Accessibility Hierarchy (Keenan and Comrie 1977). Relative clauses in Basaá form a natural class with demonstrative modifiers, as they cannot co-occur in relative clauses involving a gap. This restriction does not obtain for relative clauses with the resumption strategy. We show that by adopting the head-raising analysis of relative clauses just for those relative clauses that include a gap; the complementarity of demonstratives and relative operators in Basaá follows. Thus, the Basaá facts provide a novel empirical argument for this analysis of relative clauses. We offer a diachronic perspective on these facts, suggesting the Basaá relative operator is at an intermediate stage of grammaticalization.