The Daughters Are Mine, The Sons Are Mine
“Grandchildren Are Like Children”
In discussing the laws of pru u’rvu, the obligation to have children, the Gemara states that “children of children are considered like children.” Therefore, if a person had grandchildren, and then his sons die, he fulfills his mitzvah through his grandchildren, and is not obligated to have more children. Based on this principle, the Shulchan Aruch rules that a grandfather is obligated to teach Torah to his grandchildren, just as he is obligated to teach his own children (Y.D. 245:3).
From the Gemara, it seems that not only are one’s son’s sons considered his own, but so too are his daughter’s sons. For this reason, the Gemara brings a proof from Lavan, who said that the sons of his daughters Rachel and Leah were like his own sons. In fact, when the Gemara asks from where we know that grandchildren are like children, Rashi explains that the Gemara asks only concerning one’s daughter’s sons. It was obvious to the Gemara that one’s son’s sons are like his own. Although the proof from Lavan was rejected, the principle is still accepted by the Gemara – that one’s daughter’s sons are like his own.
Rabbeinu Bachaye writes that Lavan’s statement, “The sons are my sons” (Bereishis 31:43) was false. Although they were indeed his grandchildren, the Talmud Yerushalmi (Yevamos 6:6) states that only one’s son’s sons are considered his own, not his daughter’s sons. The Midrash Rabba (Vayigash 94:6) writes of the verse, “Yaakov and all his descendants came to Egypt,” that his son’s sons were listed as his sons, but not his daughter’s sons. (This contradicts the Talmud Bavli in our sugya. It is interesting to note that Rabbeinu Bachaye favored the opinion of the Talmud Yerushalmi over the Talmud Bavli.)
Lavan Kissed his Sons and Daughters
The Maharil Diskin asks why the Gemara does not bring a proof that grandson’s through one’s daughter are like sons from this posuk: “Lavan kissed his sons and daughters.” This was not just Lavan’s claim. Here the Torah itself calls Bnei Yisrael his sons.
R’ Diskin answers that this verse is in fact a continuation of the previous one: “Yaakov slaughtered animals on the mountain… and Lavan kissed his sons and daughters.” The pronoun “his” does not refer to Lavan. “His” refers to Yaakov, whose sons Lavan kissed.
Learning Torah with Grandchildren
The accepted halacha follows the conclusion of our sugya, that one’s son’s daughters are like his own. Therefore, if one has grandsons from his daughter, and then his son dies, he need not have more children, since he has fulfilled the mitzvah of pru u’rvu.
However, regarding the mitzvah to learn with one’s grandchildren, the Shach cites a question of the Kesef Mishna. If a person is approached by two prospective students, one of whom is his son, his son takes priority. If one is his grandson, he also takes priority, since one’s son’s sons are like his own. However, if one of them is his daughter’s son, does he also take priority? Are one’s daughter’s sons like one’s own? The Kesef Mishna leaves this question unanswered.
The Rema (240:24) rules that one must honor his father’s father. However, the Vilna Gaon (s.k. 34) notes that one need not honor his mother’s father. This also implies that one’s daughter’s son is not like his own, and conversely, his mother’s father is not like his father.