Bava Basra Daf 136 בבא בצרה דַף 136

The next Mishnah states that if one writes his properties to his son, but wants to retain the produce during his lifetime, Rebbe Yehudah says: צריך שיכתוב "מהיום ולאחר מיתה" – he must write that the gift should take effect “from today and after death.” The Gemara explains that this indicates that the גופא – principal (i.e., the land itself) is acquired by his son immediately, and the פירא – produce is acquired only after he dies. Rebbe Yose argues and says he does not have to write "מהיום". When Rabbah bar Avuha was ill, Rav Huna told Rav Nachman to ask him if the halachah follows Rebbe Yose. Rav Nachman responded that he did not even know Rebbe Yose’s reasoning; how can he ask if the halachah follows him? Rav Huna said he would explain Rebbe Yose’s reason afterwards. After Rabbah bar Avuha told Rav Nachman the halachah follows Rebbe Yose, Rav Huna explained that Rebbe Yose holds: זמנו של שטר מוכיח עליו – the שטר’s date proves when it should take effect. There is no purpose in writing a date in the שטר unless he wants it to take effect from that time.

The Mishnah taught, where a father gifted his son property “from today and after death,” such that the son owns the גוף and the father retains the פירות", that neither can unilaterally sell the land now, because of the rights of the other. If the father sells it, the buyer enjoys his rights (of the produce) until the father dies. If the son sells it, the buyer has nothing until the father dies (when the son would inherit the land).

Amoraim discuss the law if the son sold the property and died before the father. Rebbe Yochanan says the buyer does not acquire the land, even when the father dies, because he holds קנין פירות כקנין הגוף דמי – ownership of the right to the property’s produce is tantamount to ownership of the principal itself. Since the father was considered the primary owner, it emerges that the son sold property which never became his, so the sale is void. Reish Lakish holds the buyer does acquire the property after the father dies, because he holds קנין פירות is not כקנין הגוף. Since the son is the primary owner, his sale is valid.

The Gemara asks that Rebbe Yochanan and Reish Lakish already argued elsewhere about קנין פירות: if one sells his field for right to its produce, Rebbe Yochanan says:  מביא וקורא – the buyer brings [bikkurim] and recites [the bikkurim pesukim], because his קנין פירות is sufficient to consider him the property’s owner. Reish Lakish says he brings bikkurim but does not recite the pesukim, because his קנין פריות is insufficient to consider him the owner. The Gemara explains that both arguments were necessary: if Rebbe Yochanan had only taught קנין פירות is כקנין הגוף in general, such as regarding ביכורים, one might still think that where one gifts his son, אבא לגבי בריה אחולי אחיל – a father forgoes more towards his son and gives him the physical property completely (although he retains the פירות, does not retain it as a קנין הגוף). If Reish Lakish had only taught that קנין פירות is not כקנין הגוף generally, one might have thought כל לגבי נפשיה – that wherever one retains פירות for himself, אפילו במקום בריה נפשיה עדיפא ליה – he cares more about himself, even vis-à-vis his son, and retains principal ownership through the פירות. Therefore, Rebbe Yochanan and Reish Lakish restated their opinions in our case.