This article explores the emergence of complex predicates in Persian with a focus on voice and transitivity. It argues that the rise of CPs is linked to the development of the verb pair “do” and “become”, which encode the features called Instigation [+INST] and affectedness [+AFF], respectively, by Næss 2007. While these features are characteristic for prototypical agents and patients, respectively, taken alone they are more general than that, making the two verbs “underspecified”, a typical characteristic of light verbs as noted by Megerdoomian 2012 and others. The distribution of the verbs “do” and “become” is parallel to the domains of the Old Iranian active and middle (mediopassive) voice; it thus mirrors the voice opposition whose morphological marking is lost within Middle Iranian. With “do” and “become” as its centre, the system integrates additional verbs such as “hold” and “give; put” on the [+INST] side and verbs of movement on the [+AFF] one. The same verbs are also used as auxiliaries for periphrastic formations such as the potential construction, the transitive preterite and the analytic passive, suggesting that grammaticalisation of auxiliaries and the development of light verbs are parallel processes the precise similarities and differences of which remain to be investigated. Here as elsewhere, the somewhat fragmentary evidence of early stages of Iranian is supplemented by data from languages that have found themselves under Iranian influence, providing details which are crucial to complete the picture.