Another classic factor in psak that causes poskim to rely on positions they wouldn’t normally rely on is hefsed – monetary loss. Shiur and sources (including many summaries from Encyclopedia Talmudit) are available: here.
That the Torah cares about the economic stability of the Jewish people is clear. There are two formulations of this that are explicitly connected by the Yerushalmi (and many Rishonim and Achronim). Specifically, the notion of HaTorah Chasah al Mamonam shel Yisrael, the Torah had pity on the money of the Jews, and the dispensation found throughout Shas in cases of hefsed merubeh, great economic loss.
The former concept explicitly appears in Shas to explain why certain mitzvoth are patterned the way they are. For example, the Gemara explains that while the Kohen Gadol uses a golden shovel for the ketoret on Yom Kippur, during the rest of the year he uses a silver one, so as not to incur extra expenses for the Jewish people. The exact parameters of this principle are unclear. As the Teshuva M’Ahava notes, there is another concept that seems to contradict it – the notion of ein aniyut bimakom ashirut, that in the Beit HaMikdash, which is supposed to show grandeur and majesty, we cannot do things that seem poor. The Noda BeYehuda suggests that there are middle ways of doing mitzvoth that are neither rich nor poor. In the above case, for example, silver is cheaper than gold, but still not cheap. This discussion highlights that there are limits to the principle of HaTorah Chasah. After all, we are expected to do mitzvoth even if they cost us money. All HaTorah Chasah tells us is that God doesn’t expect or want us to go so far as to destroy ourselves financially. This acts as a model to understand the limitations of the related principle of hefsed. Financial loss is a legitimate reason to try to be lenient, but the loss must be significant enough to warrant a kula, and the kula must be tenable. There are always going to be cases, however, where one must lose or spend money to keep the Torah properly.
In addition to being the basis of certain details in some mitzvoth, HaTorah Chasah is sometimes the impetus behind entire mitzvoth or takkanot. For example, the Radbaz says that God allows people to test him by the mitzvah of maaser – meaning to give tzedakah and expect something in return from God, because He wants to encourage people to support the poor. This is despite the fact that many authorities believe there is a prohibition in general to test God. Similarly, the allowance to work on Chol HaMoed to prevent a loss seems to be driven by this principle. Lastly, many takanot were set up to protect the Jews financially, such as that recorded by Mishna Berurah, that people were not to buy fish for Shabbos when the sellers were price gouging.
Two possible limitations that are suggested for this rule are either that 1) it only applies to the community, but individuals can spend as much money on a mitzvah as they want (Chafetz Chaim in Likutei Halachos) or 2) it only applies to positive commandments. Negative commandments, which one would have to give up all his money to avoid, do not have the same dispensations (Mahartz Chayes).
Most of the shiur focused, however, on the question of hefsed – when in psak can you be lenient to prevent monetary loss. Here, we see that the classic rules of pesikat halacha bishaat hadechak that we saw a few weeks ago apply (here). In fact, this is the classic case brought by the Rashba. Thus, the same questions apply – does it only apply by derabanans (Shach) or even Diorayta (Bach)? Does it apply against the rov or not (Bach vs. Shach)? Other questions are also raised – can we be mekal if we need to rely on two kulot? What if there is loss of money and kavod Shabbos, can we be even more lenient? As I mentioned from R. Lichtenstein before , I think the general rule is that the greater the pressure, the less likely a position we can rely on if we need to. If the pressure is not great, we stick to positions that are more likely. It is a sliding scale. The only thing we need to keep in mind is that if a position is totally wrong, nothing can get us to rely on it.
The Rama in Toras Chatas adds another caveat. In many cases, we are machmir beyond the letter of the law. In these cases, the Rama rules that if there is a monetary loss, we rely on the lenient position. He adds that even if there is no objectively large loss, but there is another pressure such as a person won’t have food for Shabbos, were are similarly lenient. However, the minhag of poskim is to explain that what drove the kula was kavod Shabbos, rather than explaining that we really think this position is mutar m’ikkar hadin.
The next question to ask is what is a great loss? Here, there are many positions who try to find formal definitions, but the mainstream position seems to be that it is subjective – the posek can figure out whether the loss is significant or not. The poskim question whether we judge this based only on the local case, or the general picture. In other words, if many people have the same Shayla on a regular basis, being machmir will cause a large net loss, but each case is not significant. The similarly question whether something is a hefsed merubeh if one partner will suffer greatly but the other won’t. What if there won’t be a loss of capital, but there will be a loss of profit?
Some poskim, based on Chasam Sofer, think that we are only lenient for the person who asked the question for whom it cause a loss to be machmir. However, others cannot be mekal. Therefore, a butcher who received a kula can sell his meat, but others cannot buy it. Many poskim reject this, as it defeats the purpose. They compare it to permitting an agunah – if she can remarry but no one can marry her, what have you gained?
Another common question is whether something is considered a hefsed merubeh if the loss is really a combination of many small losses. For example, if one dish of china is not significant but the set is, is it a loss or not. R. Moshe Feinstein rules that it is, but a teshuvah of R. Akiva Eigar says otherwise (in the case of the china, he may also view the set as one unit, but you get the point.)
Parenthetically, R. Ovadiah took HaTorah Chasah as a mantra, and encouraged kula in many cases because of it. This was especially true Pesach time, where he rejected the minhag of some sfardim to be machmir like the Rama against the Mechaber.
These are just some general guidelines, but they should highlight the importance and complexity of the topic.