The Gutnish-specific si-passive combines be or become with a participle, directly followed by the element si. Unlike regular periphrastic passives, si-passives focus on the process rather than the result, opening up the construction for unergatives, which are unattested in the regular type. However, si-passives are quite limited when it comes to the subject. Internal arguments can only become subjects if they strand a preposition or a particle. Otherwise, the subject is expletive. I argue that si is part of the participle ending in Aspo, where its phi-features block agreement with the internal argument, trapping it in situ and depriving Aspo of a link to the result of the event. Originally a reflexive, si was reanalysed as a marker of the participle rather than the infinitive in contexts where conjugational changes had made them ambiguous. These changes never affected Fårö, where the si-passive is thus correctly predicted to be absent.
