If in a language there are two classes of sentences such that there is ergative-type verb agreement in one but not in the other type and the semantic property whose respective presence and lack characterizes the two classes is perfectivity, then it is in the class of perfective sentences that ergative verb agreement will occur, rather than in the other class.
Standardized
Whenever there is more than one alignment type of verb agreement, one being ergative and the other non-ergative: ergative verb agreement occurs in perfective sentences, and non-ergative verb agreement occurs in imperfective sentences.
Cf. #898.