This paper focuses on the Experiencer Object (EO)/Experiencer Subject (ES) alternation in Polish. This alternation is viewed here as distinct from the causative/anticausative alternation, because eventive EO verbs do not pattern like change of state (COS) verbs, and their reflexive ES alternants are unergative, not unaccusative. Eventive EO verbs share a common base with their ES counterparts, which corresponds to an unergative vP, with the experiencer merged in a low external argument position, viz. Spec, vP (Tollan 2018), not in Spec, VoiceP. The difference between causative EO verbs and their ES cognates lies in the Voice layer; in the former, the causer argument occupies the specifier of thematic VoiceP, while in the latter the Voice is expletive, filled with the reflexivemarker się. Despite sharing the common base, eventive EO verbs and their reflexive ES variantsare not derivationally related by a syntactic rule, as neither of the two structures can be treated as the basic one. The same reflexive marker with the same function and structural position is foundin Polish anticausatives, which also share a common base with their causative counterparts. The common base, this time, however, corresponds to an unaccusative, not unergative, vP.