The Gemara in Menachos (41b) says: “It was stated: Rav holds that one may not use one candle to light another, and Shmuel holds that one may. […] Abayei said: With regard to every law but these three (including the one quoted above) [Rabba] followed the opinion of Rav, but for these three he followed Shmuel.” Rashi and others point out that the Gemara refers to the candles lit on Chanukah. (See the poskim in Orach Chayim 674 regarding other obligatory lightings.)
Rabbeinu Gershom on the Gemara explains like Rashi, that the discussion here is about Chanukah candles, but adds an explanation of Rav’s position. He writes: “[According to Rav] one may not light one candle with another because one thereby diminishes the [object of] mitzvah.” At first glance this seems innocent enough. He simply intends to explain that Rav’s objection stems from a concern that using a mitzvah-purposed candle to light other candles – even other mitzvah candles – causes the former to be somehow diminished.
Those familiar with the main dapim dedicated to the laws of Chanukah (found in Maseches Shabbos), however, will wince at R’ Gershom’s comment. The Gemara in Menachos quoted above appears nearly verbatim in Shabbos (22a-b), followed by a lengthier conversation of the topic. The Gemara quotes the same three disputes between Rav and Shmuel regarding which Abayei says that Rabba followed Shmuel, and then continues by investigating the reasons behind the dispute regarding Chanukah candles. The following is the immediate continuation of this Gemara:
“One of the rabbis sat before Rav Ada bar Ahavah and said: The reasoning of Rav [in positing that one may not light one candle from another] is because of bizui mitzah, the disgracing of a mitzvah-purposed item. (Rashi explains that one would light a woodchip or the like from the first candle and then use it to light the second candle. This is a bizayon because he is lighting the woodchip, an item not included in the mitzvah, from a mitzvah flame.) [Rav Ada bar Ahavah] responded: Do not listen to him! The reasoning of Rav is [rather] that by doing this one is being makchish the mitzvah.” For the moment we will take Rashi’s explanation of this last line for granted, as he explains that using the mitzvah flame to light another candle gives off the appearance that one is removing something from the mitzvah item.
To this point it seems that Rabbeinu Gershom back in Menachos is well-founded. He simply explains the Gemara there according to the understanding of Rav Ada bar Ahavah. The Gemara’s continuation, however, will make us think twice about this. The Gemara makes two attempts to disprove Rav Ada, the first of which is unsuccessful. The Gemara’s second attempt is its presentation of a law quoted by Rav Sheishes regarding the daily menorah lighting in the Mishkan. Rav Sheishes rules that one of the candles of the menorah would be used to light the others. This surely means that we are not concerned for kichush mitzvah, apparently disproving Rav Ada’s explanation of Rav’s position earlier in the Gemara. This objection to Rav Ada is accepted, and the Gemara concludes that “kushya!,” indeed the question is a good one.
Rabbeinu Gershom’s comment in Menachos should now spark some degree of queasiness. If the Gemara in Shabbos ultimately disproves the explanation of mitzvah-item diminishment, why did Rabbeinu Gershom use it to explain Rav? Was he not aware that the Gemara disproved this?
In understanding Rabbeinu Gershom it seems appropriate to consider the way in which the poskim relate to this discussion. The Aruch Hashulchan (OC 674:1) begins this topic with a particularly notable phrase. He says: “One may light one candle from another, as this is not a disgrace to the mitzvah because that which he is lighting from the holy item is holy as well. And even though it may seem as though he is diminishing from the fuel of the first flame by lighting the second flame from it, this is not a problem because in reality he is not removing anything from the first flame. As such we are not to any extent careful to avoid lighting one candle from another.”
Clearly, the Aruch Hashulchan understands the possible concern of akchushei mitzvah – i.e. Rav Ada bar Ahavah’s explanation of Rav – in the same way Rashi did above. Rashi said that the issue of akchushei mitzvah is that by lighting the second candle from the first one gives the impression of detracting from the first. In other words, even according to Rav Ada’s concern, the issue is not that one is really detracting, for indeed no detraction occurs. The problem is only one of appearances. As such, when the Gemara rejects this concern, it is essentially saying this appearance is not a problem. We do not care that onlookers will think he is in some way diminishing the flame. This is all reflected by the Aruch Hashulchan. He goes out of his way to explain that we do not care about akchushei mitzvah because in reality no kichush occurs.
He implies, however, that if there were a valid concern that lighting the second candle would diminish the first, we would indeed say that there is a problem of kichush mitzvah. In other words, he does not reject the essential concern of kichush mitzvah, but rather dismisses the notion that the concern is relevant to this situation.
Perhaps the Aruch Hashulchan would therefore admit that according to Ritva (in Shabbos there), who explains kichush mitzvah as a valid, reality-based concern, there would indeed be a problem of lighting from one candle to another. (Ritva explains that the momentary increase in heat caused by the igniting of the second candle causes excessive expenditure of the first candle’s fuel.) We would then suggest that the Gemara’s ultimate rejection of Rav Ada – “kushya!” – is not at all an absolute rejection as we assumed before. Instead, this exclamation should be understood in the way of various Rishonim (see Rashi to Sanhedrin 72a, as well as Rabbeinu Chananel quoted by Rashbam and Ritva to Bava Basra 52b), that “kushya” merely means: answers to the present question exist, but are not completely comforting. Had the Gemara wished to reject Rav Ada absolutely, it would have said not “kushya” but “teyuvta” – a phrase understood by the aforementioned Rishonim as an absolute refutation. (See Ritva to Bava Basra there who refers to a tradition from a particular scholar in Provence who had answered every “kushya” left unanswered in Shas. See also a comment of the Hagahos HaGriv on the “Kitzur Kelalei HaTalmud” printed in the back of Berachos Gemaras alongside Rav Shmuel Hanagid’s “Mavo HaTalmud” – c.f. “Kol makom she’amar ‘kushya’” – where he claims to himself have solved all unanswered “kushyos” in Shas.)
If this is correct, we can now understand the comment of Rabbeinu Gershom we began with. We were troubled by R. Gershom’s consideration of akchushei mitzvah as the concern behind Rav’s opinion, because the Gemara in Shabbos seems to upend this line of thought. But we now see that the Gemara’s rejection might only be absolute according to Rashi’s understanding (if even his), that there is not actually any kichush and therefore no concern. According to Ritva’s understanding, though, it would stand to reason that the Gemara’s dismissal of the concern is only an initial rejection, leaving room for Rabbeinu Gershom to still understand Rav’s opinion to be concerned for this.
(NOTE: After writing this article I noticed that the Aruch Hashulchan’s concluding words there seem to imply the above understanding of his opening line. The reader is invited to see his words there and consider whether or not they say what has been proposed here.)