פירוש על קידושין 11:10

The Talmud answers that if he said nothing, and they were talking about betrothal, then they would be married. But since he used one of these confusing formulas, she might not have understood what she was saying yes to—maybe she was agreeing to work for him. Therefore, they are considered of doubtful validity. In such a case the couple would either need to redo to betrothal or get divorced.