In English, some causation verbs take a [DP + uninflected VP] complement. Within this class, make and let allow the VP to be omitted; have does not: First I made/let/had John eat dinner, then I made/let/*had Mary. Our empirical contribution is twofold. First, ‘VP-omission’ involves Null Complement Anaphora. Second, the thematic roles of the causer and causee are more restricted with VPO than when the VP is present – specifically, both must be agents. Our analysis ties these two points together: the null pro-form of NCA is selected by a dedicated Voice head ‘VoiceVPO’, which is subject to a ‘Voice Uniformity’ condition. Finally, we argue that the amelioration of VPO with experiencer-have follows from our analysis.