Yesterday we saw that the Turei Even understood the Rashba to be saying that failing to fulfill a mitzvah would be a violation of bal tigra. Turei Even argued that this is incorrect. It's doing a mitzvah in an incomplete way which is bal tigra, not failing to do the mitzvah at all.
The T.E. raised two questions. I want to focus on the second one. He proved his point from a gemara in Sukkah :
אמר מר לא מצא אתרוג לא יביא לא רמון ולא פריש ולא דבר אחר פשיטא מהו דתימא לייתי כי היכי שלא תשכח תורת אתרוג קמ"ל זימנין דנפיק חורבא מיניה דאתי למסרך
The gemara has a hava amina that if there is no esrog available, take some other fruit so that you at least remember that there is a mitzvah of lulav and will do it properly next year. According to the Rashba, how can you have such a hava amina? Taking only 3 of the 4 minim does not fulfill the mitzvah, so it would violate bal tigra. Can you violate a lav just to have a zecher?!
My wife's grandfather quotes a solution to this question in the name of his BIL R' Yosef Holzberg which is echoed by the Sefas Emes in his chiddushim on R"H. When you have an incomplete mitzvah and are in violation of bal tigra, yesh lachkor the following lomdish chakira: does the issur stem from what you are *doing*, or does the issur stem from what you have *failed to do*? Is it the mitzvah action which is the problem because it will prove to be defective; or is the piece that you left out which is the issue?
The answer is black on white if you read the classic case of bal tigra (R"H 28) carefully:
דתנן הניתנין במתנה אחת שנתערבו בניתנין מתנה אחת ינתנו מתנה אחת מתן ד' במתן ד' ינתנו במתן ד' מתן ד' במתן אחת ר"א אומר ינתנו במתן ד' רבי יהושע אומר ינתנו במתן אחת אמר לו ר"א הרי הוא עובר על בל תגרע אמר לו ר' יהושע הרי הוא עובר על בל תוסיף א"ל ר"א לא נאמר בל תוסיף אלא כשהוא בעצמו אמר לו ר' יהושע לא נאמר בל תגרע אלא כשהוא בעצמו ועוד אמר רבי יהושע כשלא נתת עברת על בל תגרע ולא עשית מעשה בידך כשנתת עברת על בל תוסיף ועשית מעשה בידך
R' Yehoshua's argument is that bal tigra entails no action: ועוד אמר רבי יהושע כשלא נתת עברת על בל תגרע ולא עשית מעשה בידך. If the issue was with what you are doing, the incomplete act, it would be a lav which has a maaseh. לא עשית מעשה בידך implies that it's what's being left out which is the issue.
Coming back to the Turei Even's proof from the gemara in sukkah: Had the issur of bal tigra been the action that will remain incomplete, then taking the lulav, taking the hadas, the arava, would be a problem. But the issur of bal tigra is in what you are missing, not what you are doing. In this case, what can you do if no esrog is available? Ones Rachmana patrei! Maybe Rashba is right, that missing an entire mitzvah potentially is bal tigra, but in this particular case you would still be off the hook.
I have a thought experiment to help illustrate this point: The halacha says that you only have to spend up to 20% of your money to fulfill a mitzvas aseh and no more, but you have to give up every penny to avoid violating a lav. Let's say a lulav and esrog will cost more than 20% of my money. I should be exempt from the mitzvah. But if I don't fulfill the mitzvah, according to Rashba, won't I be in violation of the lav of bal tigra, and therefore shouldn't I have to give up every penny to avoid the lav?
It must be that since the halacha says that I don't have to spend more than 20%, I'm not in violation of the lav if I don't do the mitzvah. So too, the same holds true if no esrog is available, I'm not in violation of anything if it is missing because I have a ptur ones.
This chiddush helps us with all kinds of things. The Minchas Chinuch (see Aruch haShulchan as well) discusses whether there is any value to eating 1/2 a k'zayis of matzah if you don't have enough for a full shiur. There is a concept of chatzi shiur by issurim. Is there a similar concept by a kiyum mitzvah? According to the Rashba, the whole question shouldn't even get off the ground. If you fail to fulfill the mitzvah, you run the risk of bal tigra!
The Chashmonaim found only enough oil for one day. The Beis Yosef suggests that having no other choice, they divided what they had into 8 parts. Miraculously, the oil burned throughout the night on each night even though it was far less than the shiur. According to the Rashba, what was their hava amina? Barring the miracle, wouldn't they be violating bal tigra by lighting less than the required shiur and failing to do a proper hadlaka?
The answer is the same for all these examples. Do what you can because the issur of bal tigra is not in what you are doing, it's in what you are leaving out. Like in the case of esrog, in these cases you have no other choice than to not complete the mitzvah and leave something out -- you are in a situation of ones. Therefore, there is no chiyuv bal tigra on what's missing.
The final example of the Sefas Emes is wearing tzitzis without techeiles. There is no bal tigra because you are ones; techeiles is not available. Therefore, you cannot be chayav for doing an incomplete mitzvah. That argument may have held true in the time of the Sefas Emes, but today, techeiles IS available. Even if you are not 100% it is the right thing, what's the downside, given that not wearing it might put you in the bind and in violation of bal tigra?