The paper describes ways of expressing causative semantics in Gban: by lexical means (suppletive pairs and lability), by periphrastic means, and by morphological means: the productive derivational suffix ‑kà with broad causative semantics. In the case of suffixal causatives from transitives, a peculiar “double object” coding pattern is observed, with two preverbal clause-level NP positions. The suffixal causative construction is hypothesized to have grammaticalized from a construction with a causative verb and an unmarked nominalization (as its object), which could itself have two left-side nominal dependents. The hypothesis is supported by a number of independent synchronic facts, including the syntactic properties of nominalizations.