As we have learned, there is a special principle that applies on Shabbat prohibiting only melekhet maĥshevet, a melakha done intentionally and thoughtfully. In this context, a disagreement arose among the Tanna’im concerning a case in which one intends to perform a certain act, but not for the sake of the object (le-gufo) upon which the melakha is performed. For example, extinguishing a fire le-gufo means extinguishing a fire in order to produce coals or so that the wick ignites more readily the next time. In both cases, the extinguishing itself achieves the desired effect. In contrast, if one extinguishes a candle in order to save oil, or because the light disturbs him, he has not done the melakha because he wants to extinguish the fire, but rather because he does not want the flame to continue burning. Thus, the melakha is she-lo le-tzorekh gufah (not for its own sake). R. Shimon maintains that since this melakha was not undertaken for its own sake, it is only prohibited rabbinically. According to R. Yehuda, however, even when one’s goal is not the melakha itself, since in fact he intended to put out the flame, he performed the melakha and transgressed a Torah prohibition (Shabbat 31b; 93b; below 16:5).
Another case: One who digs a hole in order to lay the foundation of a house has performed the melakha of Boneh, and one who digs a hole to plant a tree has performed the melakha of Ĥoresh. Yet if one digs a hole because he needs the dirt, he has performed the melakha by digging, but not for the sake of the digging itself. In R. Shimon’s opinion, since his intention was to remove dirt and not to dig a hole, he has transgressed a rabbinic prohibition but not a Torah prohibition; according to R. Yehuda, since he did intend to dig, he has transgressed a Torah prohibition.
Although all agree that one may not perform a melakha even if it is she-eina le-tzorekh gufah, there is an important ramification of this difference of opinion. If melakha she-eina tzerikha le-gufah is forbidden rabbinically, then there are instances when it would be permitted, whereas if it is prohibited by Torah law, there would be no grounds for leniency.
The vast majority of poskim rule that a melakha she-eina tzerikha le-gufah is rabbinically prohibited (R. Hai Gaon, Rabbeinu Ĥananel, Ramban, Rashba, and Rosh). However, since some are stringent (Rambam, MT 1:7), and since the only difference between this action and an action that is prohibited by Torah law is the intent that informs it, melakha she-eina tzerikha le-gufah is considered more serious than other rabbinic prohibitions.
. SA 316:8 and 334:27 cite the opinion of most poskim anonymously, and then cite Rambam’s opinion by name, indicating that the ruling is in accordance with the majority of the poskim (MB 334:85 and Yabi’a Omer, 4:23:1 rule similarly). However, we are more stringent when it comes to a melakha she-eina tzerikha le-gufah than with other rabbinic prohibitions, since the performance of such an action is identical to the performance of a Torah prohibition. The only difference is in one’s intention (Tosafot, Shabbat 46b, s.v. “de-khol”; SHT 278:4).The difference between psik reisha and melakha she-eina tzerikha le-gufah is that in the former, the person is interested in the prohibited result, and therefore it is forbidden by Torah law, while in the case of a melakha she-eina tzerikha le-gufah he is not interested in the forbidden result. This is why according to most poskim, a melakha she-eina tzerikha le-gufah is only rabbinically prohibited. Therefore, in all cases of psik reisha de-lo niĥa lei, the prohibition is only rabbinic. However, if one cuts off the head of a bird, he cannot claim that he is unhappy with the bird’s death, as that would be disingenuous. This is the position of Tosafot (Shabbat 103a, s.v. “be-ar’a”) and Rambam (as quoted in the commentary of Rabbeinu Peraĥya on Shabbat 42a). One can further explain that in the case of psik reisha the permitted activity is secondary to the forbidden one and therefore nullified, while a melakha she-eina tzerikha le-gufah there is not nullified. Therefore, R. Shimon rules that the prohibition is rabbinic. One can further explain that a melakha she-eina tzerikha le-gufah consists entirely of one action, so when performed for permitted ends, his objectives cancel the intention to do something prohibited. However, a psik reisha produces two distinct results, so one’s intent to achieve the permitted result does not cancel out the prohibited second result. See Harĥavot 9:6:6.