Hello Rabbi. First of all, it is not obvious that this is a detail within the laws of the commandment of “you shall eliminate it,” especially according to one who claims that it takes effect only from the sixth hour onward. Besides, I would say that what does not need a source is declaring it ownerless, because it is obvious that this helps, since there is no longer ownership over that leaven. For that, presumably, no special reasoning is needed, since the whole prohibition is only about my leaven. Therefore the mechanism of declaring it ownerless is obviously effective so as not to violate “it shall not be seen” and “it shall not be found.” Now the Sages come and say that there is a way to sever ownership specifically with regard to leaven (and I also do not know from when it is effective—does it work even a week before the sixth hour, or only from the eve of the 14th?), and this way is different from declaring it ownerless. So it does not sound logical to me that the Sages would think this is correct purely by reasoning, unless one really explains that they are simply interpreting the commandment of “you shall eliminate it.” And about that I am asking: what is the source that this is indeed what they are doing? I saw that Rashi writes this, but where does he get it from? Thank you, and happy holidays!

I do not understand what other reason there would be to do nullification. This is elimination, and perhaps also avoidance of violating “it shall not be seen” and “it shall not be found.”
If logic indicates that I do not violate the prohibition with regard to leaven that is not mine, and therefore declaring it ownerless helps, similar reasoning says that nullification should help.

But where did they come up with this? Meaning, how did they understand that this is what “you shall eliminate it” means? The Rabbi does not have to answer if he feels he has exhausted the point. Thank you very much for all your work!

I do not understand the question. They did not invent anything. The Sages understood by reasoning that this is elimination.

So then what is the dispute among the Sages whether it must be by burning or whether it can be destroyed in any way? Do we not see from there that they understand elimination to be an actual physical act?

The Tannaim disagreed regarding the manner of eliminating the leaven. If one performed nullification, then by that it is eliminated and there is no need to destroy it. The Sages enacted rabbinically that even if he nullified it, he should nevertheless destroy it physically (lest he eat it). Beyond that, there is significant leaven for which nullification is ineffective (because he does not genuinely intend to nullify it), and for that physical destruction is required.

Interesting. I am now reading your lecture summaries on tractate Pesachim (the ones by the doctoral students). We would also be happy if you return to this topic in a lecture series one of these days. Thank you, Rabbi, for the response!