פירוש על קידושין 91:4

If the previous baraita referred to a case where he seduced her without the intent to marry her, then we learn the same thing in another baraita. This baraita requires that the seducer betroth her before marrying her. But if he seduced her with the intent to betroth her, then why does she need another betrothal. She is already betrothed! Thus the Torah refers to a situation where he did not seduce her for the sake of marriage.

Abaye argues with R. Joseph. Even if the man seduced her with the intent of betrothal, she still needs kiddushin with her father’s knowledge. Thus this latter baraita could refer to a case where the seducer had the intent of betrothal and would not be a support for Rav’s interpretation of the first baraita.