Kiddushin, Daf Kaf, Part 1
Introduction
The Talmud continues to discuss whether a father can sell his daughter to his relatives.
תני חדא מוכרה לאביו ואין מוכרה לבנו
ותניא אידך אין מוכרה לא לאביו ולא לבנו
One [baraita] taught: He may sell her to his father, but he may not sell her to his son.
Another [baraita] taught: He may not sell her to his father or to his son.
The baraitot both agree that a father may not sell his daughter to his son (I can just imagine how this would play out in my family!). But one baraita says he may sell her to his father.
בשלמא אינו מוכרה לא לאביו ולא לבנו כרבנן אלא מוכרה לאביו ואין מוכרה לבנו כמאן לא כרבנן ולא כרבי אליעזר
It makes sense to teach He may not sell her to his father or to his son for this agrees with the sages.
But he may sell her to his father but he may not sell her to his son with whom does this agree; neither with the sages nor with R. Eliezer?
At the end of last week s daf we saw a dispute between the rabbis and R. Eliezer the former hold that he may not sell her to his relative, while the latter holds that he may. So the second baraita agrees with the rabbis, but with whom does the first baraita, the one that distinguishes between the father and the son, agree?
לעולם כרבנן מודו רבנן היכא דאיכא צד יעוד:
In the end it follows the sages: The sages agree [that he can sell her] where there is a possibility of designation.
The baraita that allows a man to sell her to his father can even agree with the rabbis who do not allow her to be sold to relatives. If a man sells his daughter to his father, the father can designate her to his other son, who is her uncle. Uncle-niece marriage is allowed according to Jewish law. Thus he may sell her to his father because designation is possible. This would not be true when it comes to selling her to his son, because she is not allowed to marry her nephew.