Le'ilui nishmas R' Aharon David Kornfeld.
Sanhedrin 41a.
"Rabi Eliezer ben Yaakov says, I heard (from my teachers; Rashi) that Beis Din hits and punishes not according to the Torah... to make a fence (siyog) of the Torah" (Rashi: That Beis Din is permitted...to punish the punishment of death, not according to the Torah. And not that they intended to transgress Torah law... but because of the need to the hour [tzorech hasho'o].)
And indeed, the Gemoro tells us that Beis Din put to death someone who rode a horse on Shabbos (which is a Rabbinic, not a Torah, prohibition).
It is known that Chachomim were permitted to cancel a Torah law by inaction (sheiv ve'al taaseh), such as shofar on Rosh Hashono Shabbos. However, they were forbidden to cancel a Torah law by action (kum ve'asei).
If so, how was the Beis Din here permitted to actively kill someone for a transgression that is not forbidden by the Torah. Killing without the Torah's permission is obviously forbidden by the Torah. So how could the Beis Din actively cancel this prohibition?
We could equally ask this question about Rabbinic lashes (makos mardus) for the transgression of Rabbinic laws. After all, it is forbidden by the Torah to injure someone for reasons not sanctioned by the Torah. How could the Beis Din actively injure someone for something not sanctioned by the Torah?
Chaim Mateh, Rechovot, Israel
1) The Gemara stresses that Chazal were not trying to cancel any prohibition. This is what the Gemara means (46a), "They did not do this in order to transgress the Torah, but rather to make a fence around the Torah." Rashi (DH v'Lo) writes that Chazal were not intending to transgress the words of the Torah and invent a new capital penalty, but what they did was only because of the needs of the hour."
2) It seems to me that this can be compared to what Resh Lakish said in Menachos (end of 99a): "Sometimes the abolishing of the Torah is actually its foundation." This is why Hash-m praised Moshe Rabeinu for breaking the Tablets. It is a terrible thing to destroy Torah, but under the circumstances that Klal Yisrael had made the Egel ha'Zahav, the only way to save the Torah was to break the Luchos ha'Bris and start all over again. This is
why Rebbi Eliezer ben Yakov said that sometimes Beis Din has to give punishments which the offenders do not deserve, because otherwise the Torah itself would be in danger.
3)
a) Malkus Mardus is not so similar to our Gemara, because our Gemara discusses occasional punishments which are carried out only for "the needs of the hour," as Rashi writes. In contrast, Malkus Mardus are a fixed Halachah which apply always for one who transgresses Rabbincal prohibitions.
b) Rav Elchanan Wasserman zt'l, Hy'd, wrote in Kovetz He'oros (Yevamos #70, DH uv'Tos') that it would seem that all prohibitions between people only apply if they are perpertrated in a destructive and malicious way, for no reason, but if they are done for a good reason, the prohibition does not apply. This is why the Rambam (Hilchos Chovel u'Mazik 5:1) writes that the prohibition against hitting another person applies only when it is done "Derech Nitzayon," in a "way of fighting." According to this, one can understand why Chazal could grant Malkus Mardus -- they are given for the constructive purpose of enforcing Rabbinical laws.
c) This is also why the Gemara in Makos 8a tells us that a father is allowed to hit his son, or a teacher his pupil, for educational purposes. Such hitting is not carried out in an aggressive way, but rather for a constructive purpose.
(See also Rav Elchanan Wasserman in Kovetz Shi'urim, Kesuvos 32a, #92.)
Kol Tuv,
Dovid Bloom