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The Biblical obligation: Biblically, if one nullifies his Chametz, and disowns it prior to the 6th hour on Erev Pesach [i.e. Bittul], he is not required to clean his house from Chametz, and the Chametz may remain in his home throughout the entire Pesach. If, however, one does not want to nullify his Chametz and disown it [or did not do so for whatever reason, and the 6th hour has already arrived], then when the time of the owning Chametz prohibition arrives [i.e. the beginning of the 7th hour], he is Biblically obligated to check and search all his possessions for Chametz and completely destroy it from the world.
The Rabbinical obligation: The Sages decreed that nullifying and disowning one’s Chametz before Pesach [i.e. Bittul] is ineffective if it will remain in one’s home, and the Chametz hence remains within one’s ownership, Rabbinically, even if one disowns it. Thus, before Pesach, one must clean all of his possessions from Chametz, just like he would Biblically be required to perform if he did not disown it. One who disowns his Chametz, but does not remove it from his property, transgresses the Rabbinical prohibition of Baal Yiraeh and Baal Yimatzeh.
The obligation of cleaning as a preparation for Bedikas Chametz: The cleaning obligation of the Sages is fulfilled by one searching his home for Chametz on the night of the 14th, as explained in chapter 4. As a preparatory step for this search, one is required to clean the home beforehand, in order so one can properly check and verify the cleansing from Chametz on the night of the 14th, when Bedikas Chametz is performed. [Thus, the Rabbinical obligation of cleaning the home for Chametz contains two steps 1) To clean the home before the night of the 14th. 2) To inspect the home when the night of the 14th arrives.]
Who is obligated to clean a home? Every Jew, man or woman, who will be living in a home over Pesach, is obligated to clean and check it for Chametz. Furthermore, even if he will not be living in the home over Pesach, he is obligated to clean and check all of his property for Chametz, unless the property will be sold to other people over Pesach, as explained in Halachas 12-13. If one does not own a home [see next regarding household members], he is exempt from this Mitzvah.
Which member of the household is obligated to clean the home: The obligation to clean the home from Chametz falls upon the father/master of the home, and not upon any of his [family members and other] dependents. [Nonetheless, they can be appointed to do so on his behalf, as will be explained in Chapter 4 Halacha 3.] However, in a case that the owner is not at home to do the search, then the obligation falls upon the dependents [even if the father did not directly appoint them to do the search].
If one lives in the house of another Jew does he have to also search for Chametz? One who will be living in another’s home over Pesach, is not required to perform his own individual cleaning and Bedikas Chametz if the owner of the home will anyways be doing so. [This applies even if one purchases and eats his own Chametz in the home.]
Being that today all Jews are accustomed to performing Mechiras Chametz through the Rav of their community, why is it necessary to clean our homes from Chametz?
Although the sale contract includes all the Chametz in the home, both the known and unknown Chametz, nonetheless, one is still obligated to perform a Bedika. Thus, those who do not clean their home for Pesach on the basis of the sale, and continue to live there as usual, are making a mistake. Several reasons can be suggested for this obligation:
1. As it is forbidden to allow even a gentiles Chametz to remain openly visible in one’s home, lest one accidently come to eat it. Thus, even when the Chametz will belong to a gentile, the Bedika still retains its purpose and necessity, which is to prevent one from coming to eat Chametz.
2. As we only rely on the Mechiras Chametz as an extra insurance, and not initially to uproot the obligation of cleaning the home from Chametz.
3. As some Poskim rule that if the Mechira is taking place on the day of the 14th, then on the night of the 14th one is nevertheless obligated to clean and check his home for Chametz.
4. As if one does not perform a Bedika, then the entire house is considered “sold” to the gentile, and it is forbidden for one to make normal use of it.
 Admur 431:2 “If rather than destroying the Chametz one wants to just nullify it and disown it, its meaningless [regarding fulfilling the Torah command] once the Biblical time of the eating and benefit prohibition of Chametz has arrived, which is from midday of the 14th and onwards, as since one is prohibited from benefiting from it, he no longer retains any rights to the Chametz, and [is thus] not his at all [anymore], therefore he can no longer nullify and disown it, [as it is no longer legally owned by him.] However, before the time of the benefit prohibition [arriving], one may nullify and disown the Chametz, and may [after doing so] Biblically leave the Chametz with him in his house throughout all the days of Pesach, as one only Biblically transgresses Baal Yiraeh and Baal Yimatzeh on Chametz that he owns which he has not disowned, as the verse states “You shall not see to you”, that your own Chametz you may not see, however you may see the Chametz of others and that is disowned.”
Other opinions: Some Poskim rule that that even if one did not check his house, and did not nullify his Chametz, he does not retroactively transgress Baal Yiraeh when he finds Chametz on Pesach, and any Chametz which he did not find on Pesach he does not transgress at all, as the Torah only prohibits one from owning known Chametz. [Magen Avraham in his understanding of Rambam and Rosh, brought in Kuntrus Acharon 433:3] We do not rule like this opinion [Kuntrus Acharon 433:3]
 Biblically, one is able to disown the Chametz until midday, which is the end of the 6th hour of the day and start of the 7th hour. However, Rabbinically, one may only nullify until the start of the 6th hour of day, as states Admur 433:30 “[The ability, to disown the Chametz until midday, is only from a Biblical perspective, however Rabbinically] once the beginning of the 6th hour of the day has arrived, one is no longer able to nullify the Chametz being that the sages decreed that from the [beginning of the] 6th hour and onwards one cannot get any benefit from the Chametz. Thus, starting from the [beginning] of the 6th hour one no longer has any portion or rights to the Chametz, and it is thus not considered his for him to be able to nullify it and disown it.”]
 The reason: As one only Biblically transgresses Baal Yiraeh and Baal Yimatzeh on Chametz that he owns, which he has not disowned, as the verse states “You shall not see to you”, that your own Chametz you may not see, however you may see the Chametz of others and that which is disowned. [ibid]
 Admur 431:3 “[The above ability to do bittul and disown the Chametz before the 6th hour, and then be able to leave the Chametz in his home, is only from a Biblical perspective, however] the sages decreed that doing bittul and disowning the Chametz is meaningless to [avoiding the prohibition of owning] the Chametz even when done before the time of the benefit prohibition arrives [i.e. the 6th hour]. Rather, they decreed that one must search after the Chametz in the holes and hidden areas, if it is common to use these areas throughout the year, and to check and remove any Chametz found within his entire property, and [destroy it or places it in a public area, as will be explained.]”
 The reason for this decree: Admur 431:4: There are two reasons why the sages made the above decree [that the Chametz may not remain in one’s home even if nullified and disowned]:
- First Reason [Rashi]: The reason why the Sages made the nullification ineffective is because nullifying and disowning the Chametz is dependent on ones thought, [meaning] that he disowns the Chametz with a full heart and remove it completely from his heart. Now, since not all people’s thoughts: Daas are alike, and it is [thus] possible that one may be lenient in this and will not disown it with a full heart, and will not remove it from his heart completely, therefore, the sages decreed that nullification and disowning is meaningless unless one actually removes all his Chametz from his property. [1st reason in Admur 431:4]
- Second Reason [Tosafos]: [The reason why they decreed that the Chametz be removed from ones property] is because people are accustomed throughout the year to eat Chametz, and due to this habit it is very possible for him to come to forget about the prohibition of eating Chametz, and he will thus come to eat Chametz if it is lying in his property on Pesach. Therefore, the sages required that one search and check for Chametz and remove it. [2nd reason in Admur 431:4]
The main reason: [Although these two reasons are mentioned] the main reason of the sages for one to search for Chametz, despite having nullified it, is because of a decree that perhaps one will come to eat it on Pesach. [Admur 433:19]
 See Admur 433:34; 434:6; 435:4
The concept of Baal Yiraeh Ubaal Yimatzeh Midivreiy Sofrim: An innovative idea brought in the Shulchan Aruch of Admur is the concept of a Rabbinical transgression of Baal Yiraeh and Baal Yimatzeh. Meaning, that if one does not check and remove the Chametz from his home he is not transgressing a plain Rabbinical decree which obligates one to do so, but rather he actually transgresses the Biblical concept of Baal Yiraeh and Baal Yimatzeh from a Rabbinical standpoint. The practical ramification between whether one learns the decree is to destroy the Chametz or learns that it is a Rabbinical Baal Yiraeh prohibition, is regarding a case that one who nullified his Chametz before Pesach and then found Chametz on Pesach. Does one say a blessing when destroying this Chametz? If one learns like the former approach, then a blessing is not recited, as we never recite a blessing prior to destroying a non-Kosher item simply to avoid coming to eat it. If, however, one learns like the latter approach, then a blessing is required, just as a blessing is recited prior to performing all Rabbinical commands. [Admur 435:4; 446:2; Kuntrus Acharon 1] Practically, Admur learns like this second approach. However, today that we in any event sell our Chametz, when Chametz is found during Pesach no blessing is said upon destroying it, as will be explained in its relevant section.
A deeper understanding: The decree of the sages that one must remove Chametz from his property was not worded as “that one must remove the Chametz from his home”. Rather it was worded that “Nullification does not help”, and then consequently one must remove the Chametz from his home, as Biblically one must remove Chametz from his home if he owns it. Thus, in a case that one has disowned and removed his Chametz into a public area before the 6th hour, then he does not need to destroy it, as even when we disqualify this nullification, one still does not need to Biblically destroy the Chametz, being that it is not in his property at all, and therefore there is no obligation to destroy it. Accordingly, it is greater understood why Admur holds of the concept of Baal Yiraeh and Baal Yimatzeh Midivreiy Sofrim, as since the sages disqualified the nullification, there remains a Biblical prohibition of Baal Yiraeh. [See Admur 445:1-2]
 Admur 433:38 “All rooms which need to be checked need to be swept prior to the Bedika. Every person should warn his family to also sweep under the beds as perhaps some Chametz has rolled under it. The reason for sweeping is because without sweeping there remains much dust [on the floor], and one is thus not able to check well. After one has swept well in all places, he has to return and check all the places with a candle, in the holes and cracks which require checking.”
 Admur 432:8; 436:3
 The reason: The reason for [why the dependents are not obligated when the father is around] is because the Chametz in the home belongs [only to the father/owner of the house and] not at all to any of the dependents. [Admur 432:8]
 The reason: When the father is not around, the dependents are obligated to clean and search the home not because they will transgress an owning prohibition, but rather Kol Yisrael Areivim. Meaning, that since the homeowner was obligated to search for Chametz all the rooms which are required to be searched [as explained in chapter 433] therefore those who remain in his home are obligated to exempt him from his obligation, as all Jews are guarantors for each other. [Admur 436:3]
 Admur 436:20
 The reason: If one will be moving in with someone else, and that someone else is the owner of the house, and that owner will check for and destroy the Chametz himself [and thus he will not be able to do a Bedika for Chametz], nevertheless, since the owner will also search and destroy the Chametz which he [the guest/boarder] used in that house from when he arrived there until Pesach, therefore, this owner is considered to be his [the guests] emissary to check and destroy his Chametz. Now, since the rule is that the emissary of a person is like himself, therefore it is considered as if he himself has destroyed his Chametz, [and he has thus fulfilled the decree of the sages to search for and destroy the Chametz of at least one home, no matter what the situation]. [Admur ibid]
 See Kinyan Torah 1:110; Moadim Uzmanim 7:162 Piskeiy Teshuvos 448:14; 436 footnote 20
 See Halacha 14 and Chapter 5 Halacha 5!
 See Admur 436:1 and Kuntrus Acharon 436:3 that one may not allow even Chametz that he does not transgress owning into his home due to worry that he may come to eat it.
 See Chapter 4 Halacha 2 in Q&A!
 See Kinyan Torah 1:110; Moadim Uzmanim 7:162Piskeiy Teshuvos 448:14; 436 footnote 20