What if someone did an act that he thought was chillul Shabbos?
Provided courtesy of Real Clear Daf
The Daf of last Shabbos (64a) discussed this question in the course of dealing with various scenarios of animals that were brought as mussaf offerings on Shabbos. It is of course obligatory to bring all of the required mussaf offerings of the day--even if it happens to be Shabbos. But what if someone offered an animal consecrated as a mussaf offering on Shabbos where the required number of offerings had already been brought? Rabbah rules that the offerer who brought that unnecessary mussaf is liable for desecrating Shabbos. What’s more, Rabbah adds, even if after two animals were slaughtered (the first one as the remaining needed offering; the second as the unnecessary offering) the blood of the first one spilled, now making the blood of the second necessary for the mussaf offering--the person would remain liable for the second act of slaughtering since at the time of the slaughtering he was unnecessarily violating Shabbos.
The Gemara later wonders about a second case: What if after the two animals had been slaughtered (and just as above, the first one was ostensibly a needed mussaf, the second unneeded) an internal examination of the first animal revealed that it was of inferior quality; a fact that--had it been known before the second animal was slaughtered--would have led us to instruct the offerer to go ahead and slaughter the fatter second animal? We can argue two ways here: Perhaps we say that since the offerer was oblivious of the first animal’s internal defect and that the circumstances as he perceived them did not warrant a second offering that he therefore is deemed to have violated Shabbos, or we can argue that since in hindsight this person’s act was necessary it therefore should not be deemed an act of chillul Shabbos.
Tosfos (heading "ואפילו") explains why this second case differs from the first one where Rabbah definitively ruled the offerer liable for the second slaughtering (even though in both cases, the second animal ended up being necessary): In the first case, at time of the slaughtering it was clearly an unneeded act whereas in the second case, had we known all of the facts, the act of slaughtering the second animal would have been deemed as necessary at the time of the act. Thus there is a strong basis to argue here that the offerer is not liable for chillul Shabbos.
Now let’s try and understand the nuance of what the Gemara is proposing here when it suggests that this person might be held liable based on his misperception in spite of the fact this this turned out to be a needed act. After all, no one would argue that if someone pulled the trigger of an empty gun that he thought was loaded that he would somehow be held liable. So what does the Gemara really mean here?
The special argument in our Gemara’s case seems to be this: If we objectively look at the raw action that was done here we have a person who slaughtered an animal on Shabbos. So the starting point is that this is an act of chillul Shabbos. However the exceptional circumstance of requiring an offering on Shabbos can potentially turn this from being an act of chillul Shabbos to a mitzva. Our Gemara is seeking to understand what it takes to push an act out of the realm of chillul Shabbos and into the realm of fulfilling an overriding need. On the one hand we can argue that the real facts on the ground should determine everything: As long as at the time of the act it was needed, it is justified. Or we can argue that we cannot use unknown information to redefine an act of chillul Shabbos into a mitzva.
To put in another way, maybe the more appropriate analogy would be to a person who indeed shot someone with criminal intent, but, unbeknownst to the shooter, the victim was about to pull out his own weapon with intent to kill: Should the shooter be fully prosecuted as a murderer or can we make an argument of self-defense? It is not obvious at all in this scenario that the murderer should be acquitted.