1) COMING HOME TO CHAMETZ
QUESTION: Rav Yehudah in the name of Rav says that one who departs on a trip more than thirty days before Pesach is not required to destroy the Chametz in his home. If he departs within thirty days of Pesach, though, he is required to destroy the Chametz. Abaye adds that he is required to destroy the Chametz only if he intends to return home during Pesach. Rava argues with Abaye and says that if he intends to return home during Pesach, then even if he leaves his home many months before Pesach, such as at Rosh Hashanah time, he is required to destroy his Chametz.
RASHI (DH Afilu me'Rosh Hashanah Nami) writes that one who leaves his home at Rosh Hashanah time with intent to return during Pesach must destroy the Chametz in his home before he departs because of the following reason. Since he will return to his home on Pesach, he will not be able to be Mevatel the Chametz on Pesach when he returns (because the Torah removes the Chametz from his ownership when it makes the Chametz forbidden, and one cannot be Mevatel an object that is not in his possession). Therefore, he must get rid of his Chametz before he departs. If he fails to get rid of the Chametz before he departs, he will transgress Bal Yera'eh and Bal Yimatzei as soon as he returns and sees the Chametz.
Why does Rashi say that as soon as he "sees" the Chametz in his possession he transgresses? Even before he arrives home and sees his Chametz, he already transgresses Bal Yimatzei by his mere ownership of the Chametz! If he does not transgress before he arrives home because he is unaware that there is Chametz in his home, then even when he sees the Chametz, he does not transgress Bal Yera'eh or Bal Yimatzei, because the Torah gives him a chance to get rid of it.
ANSWER: The MAHARSHAL answers that Rashi does not mean that he transgresses as soon as he sees the Chametz. Rather, Rashi means that if he did not know that there was Chametz in his home and now when he returns he finds Chametz there, he will transgress Bal Yera'eh and Bal Yimatzei if he delays even a short moment before he destroys it. (This is consistent with Rashi's explanation later (6b, DH v'Da'ato Alei).) Before he comes home and sees the Chametz, he certainly does not transgress, because it was not in his control to do anything about Chametz which he did not know about, and he did not have an obligation to check for Chametz because he left his home such a long time before Pesach.
2) THE MECHANISM OF "BITUL CHAMETZ"
OPINIONS: The Gemara says that the act of Bitul is effective to get rid of Chametz so that one does not transgress the prohibitions of Bal Yera'eh and Bal Yimatzei. Elsewhere (7a, 8a, 49a), the Gemara says that even Bitul b'Lev (non-verbal, mental Bitul) suffices.
In what way does Bitul work to "destroy" Chametz such that the owner does not transgress the prohibitions of Bal Yera'eh and Bal Yimatzei?
(a) TOSFOS (4b, DH mid'Oraisa) explains that Bitul is a form of Hefker. Bitul renders the Chametz ownerless. Since the Chametz no longer belongs to its former owner, he may retain it in his home during Pesach.
(b) The RAN at the beginning of Pesachim proves that Bitul is not a normal form of making Chametz become Hefker, because the wording prescribed for Bitul ("this Chametz should be like the dust of the earth") makes no mention of Hefker.
The Ran asks further that Rebbi Yosi in Nedarim (45a) maintains that when one makes his object Hefker, the object does not leave his possession until someone else takes it. According to Rebbi Yosi, if Bitul Chametz works because it is a form of Hefker, it should not be effective at all, since the Chametz remains in his possession until someone else takes it.
Moreover, we never find that a declaration of Hefker is effective when it is done mentally. It must be done verbally in order to take effect. How, then, does Bitul work when done mentally, in one's heart?
Because of these questions, the Ran explains that Bitul works in the following way. When Pesach arrives and a person owns Chametz, in theory he should not transgress Bal Yera'eh and Bal Yimatzei because the Chametz is not his anymore. When Pesach arrives, the Torah forbids him to benefit from his Chametz (it is Asur b'Hana'ah), and thus he is no longer considered the owner of the Chametz. However, the Gemara here says that even though Chametz should not be considered in its owner's possession once Pesach arrives, nevertheless the Torah puts it back into his possession so that he will transgress Bal Yera'eh and Bal Yimatzei. Consequently, in order to get the Chametz out of his possession, it is not necessary to declare the Chametz as Hefker with the normal declaration of Hefker. Rather, he merely needs to prevent the Chametz from being put back into his possession after it has become Asur b'Hana'ah.
Therefore, all he needs to do is decide that he considers his Chametz worthless. If he considers it worthless, then the Torah does not put it back into his possession when Pesach arrives, and he does not transgress Bal Yera'eh and Bal Yimatzei. Bitul is not a normal form of Hefker, because the Chametz is already out of his possession. Bitul involves merely preventing the Chametz from returning to his possession.
(c) RASHI (4b, DH b'Bitul b'Alma) and the RITVA explain that Bitul is unrelated to Hefker. When the Torah says "Tashbisu," it means that one must either burn the Chametz, or one must decide that it is valueless to him. When one declares in his mind that his Chametz is like dirt, his Chametz is not considered food anymore and is not Chametz. "Tashbisu" means that one must either physically destroy the Chametz or mentally destroy it by making it no longer considered a food. This also appears to be the opinion of the RAMBAM (Hilchos Chametz u'Matzah 2:2) according to the MAHARIK (Shoresh 142).
HALACHAH: The MISHNAH BERURAH (434:8), based on the BACH, says that when a person is Mevatel his Chametz he should say, "... it shall be nullified and be Hefker like the dust of the earth." He should mention "Hefker" because of the opinion of Tosfos. Many of the texts of Bitul Chametz used today mention Hefker only in the declaration used during the day at the time when the Chametz is burned. The declaration at night, after Bedikas Chametz, includes only the words, "... it shall be like the dust of the earth," with no mention of Hefker. This custom is a compromise intended to satisfy both the opinion of Tosfos (that Bitul is a form of Hefker) and the opinion of Rashi and the Ran (that Bitul is not a normal form of Hefker).
3) "BITUL CHAMETZ" BEFORE THE FESTIVAL
QUESTION: The Gemara says that Bitul Chametz is performed after Bedikas Chametz due to the concern that one might find a piece of Chametz during Pesach, when he can no longer be Mevatel it. The Rabanan enacted that before Pesach, after Bedikas Chametz one should also perform Bitul Chametz, so that any Chametz he might find during Pesach will not belong to him and he will not transgress the prohibitions of Bal Yera'eh and Bal Yimatzei.
Why exactly were the Rabanan concerned that one might find Chametz on Pesach? Although it is true that one who finds Chametz on Pesach cannot be Mevatel it, he is able to dispose of it by burning it immediately. If he finds Chametz on Yom Tov or on Shabbos when he cannot burn it, he does not transgress at all. He is considered an "Ones" because the circumstances are beyond his control, since the Torah does not permit him to be Mevatel or to burn the Chametz on that day. Why, then, were the Rabanan concerned that one will not be able to do Bitul on Pesach?
(a) RASHI (DH v'Da'ato) answers that if a person finds Chametz in his possession on Pesach, he might hesitate a few seconds before he burns it. Had Bitul been possible on Pesach, there would have been no need for concern; the person who finds Chametz would not hesitate to proclaim that he considers the Chametz worthless, since he does not need to physically destroy it. However, since the Halachah states that he cannot be Mevatel it on Pesach but rather he must destroy it, the Rabanan were concerned that he might hesitate before he destroys an item of value.
(b) TOSFOS (29b) explains that a person who finds Chametz and destroys it during Pesach does not transgress Bal Yera'eh and Bal Yimatzei even if he keeps it in his house for a few days, as long as he burns it before the end of Pesach. This is because the prohibition of Bal Yera'eh is a "Lav ha'Nitak l'Aseh" -- a prohibition which can be rectified by the performance of a Mitzvas Aseh (in this case, the Mitzvas Aseh of "Tashbisu," to destroy the Chametz). One corrects the wrongdoing of having Chametz in his possession by fulfilling the Mitzvas Aseh of "Tashbisu."
According to Tosfos, there is no concern that one will hesitate for a few moments and transgress Bal Yera'eh and Bal Yimatzei before he burns the Chametz. As long as he eventually burns it, he does not transgress the prohibitions. Why, according to Tosfos, did the Rabanan require that one perform Bitul before Pesach? Even if he finds Chametz in his house on Pesach, he simply can burn the Chametz when he finds it, and even if he delays burning it he does not transgress Bal Yera'eh and Bal Yimatzei.
According to Tosfos, it must be that since burning Chametz requires physical preparation (such as collecting wood and making a fire), the Rabanan feared that one would delay burning it until he has collected the wood, and then he might forget to burn it altogether. Had Bitul been possible, there would have been no concern that one might forget to perform Bitul, since Bitul can be done immediately and requires no preparation. However, since Bitul cannot be done on Pesach, the Rabanan enacted that one must be Mevatel his Chametz before Pesach.