This paper investigates the extent to which the phenomenon of transitivity contributes to syntactic organization in Ao, a Tibeto-Burman language of north-east India, by considering its manifestations from a pragmatic perspective. Agentive case marking is found to be the only formal correlate of transitivity in this language. This serves an obligatory marking function on actor arguments of verbal clauses expressing the habitual activity of a referent, and agentive marking is also consistently used to distinguish the causer argument of causativized predicates. However, in all other types of clause structures its use is pragmatically determined. Transitivity thus appears to be a construction-based phenomenon that has grammaticalized for only some aspects of Ao clausal syntax.