The Basis for Bedikat Chametz
The first mishna of Masekhet Pesachim begins by declaring the appointed time and method for performing bedikat chametz: "On the eve of the 14th [of Nissan], chametz should be searched [for] by the light of the candle." Though the mishna asserts the obligation, it does not inform us of the basis for this mitzva. One might have attributed bedikat chametz to the well-known and unique issur known as bal yeira'eh. Unlike all other prohibited foods, chametz on Pesach may not even be held in reserve. The Torah legislates against not only eating or deriving hana'a (benefit) from chametz, but keeping it in one's possession, as well. Presumably, the purpose of bedika is to rid one's property of chametz, thereby rendering a chametz-free state which accords with the demands of bal yeira'eh.
However, a gemara a few pages later (4b) clearly repudiates this simple understanding. The gemara (4a) describes several individuals who are not believed in general areas of halakhic testimony (children, slaves) yet might be believed to testify about bedikat chametz - whether or not a particular house has already been searched. As the gemara rationalizes, since the entire requirement of bedika is merely Rabbinic in nature, the Rabanan extended special reliability to those who are normally not believed. This gemara clearly establishes bitul (verbal renunciation of chametz) as sufficient – on a Biblical level - to address the concern of bal yeira'eh. What, then, is the function of bedikat chametz?
Tosafot assert the obvious position: bedika is purely a Rabbinic institution geared toward ensuring against potential problems which may arise in the wake of bitul. Tosafot look to the issur akhila of chametz and explain that even though bitul successfully solves bal yeira'eh, the chametz remains prohibited to eat. By not physically eliminating the chametz, a person runs the risk of eating it on Pesach, thereby violating an issur karet. The Rabanan demanded bedika to protect against this scenario. Tosafot, of course, is troubled by the obvious question: Why did the Rabanan worry about the presence of chametz and require its removal, but did not legislate against the possession of other types of forbidden food? They suggest certain reasons for the particular anxiety about chametz, but ultimately the question seems more compelling than the answers.
Other Rishonim suggest alternate functions for the Rabbinically-ordained bedika. Rabenu Peretz suggests that the Rabanan were concerned that a person would forget to perform bitul. As it requires no active performance, bitul might easily be neglected. By demanding bedika, the Rabanan ensured a more secure mechanism for the actual disposal of chametz and avoidance of bal yeira'eh. The Or Zarua quotes an opinion that bedika was instituted due to the concern that one's bitul would be subsequently revoked (see the peirush of Rabenu Ovadia Mi-Bartenura on the first mishna in Pesachim for an additional supporter of this opinion). This position assumes that bitul can be cancelled – an idea which might not be acceptable within all definitions of bitul. In any event, all these positions assume that bedika was instituted to address bal yeira'eh itself rather than fears that the chametz will be eaten.
Yet, this entire approach may be challenged by several gemarot which derive halakhic details of the bedika exercise from various pesukim. The gemara (7b) derives the use of a candle from several pesukim associating a candle with the process of searching, while the gemara (10b) explores the time of bedika based upon other pesukim. If bedika were purely mi-derabanan, it is unlikely that its details should be determined based upon pesukim. Though we might view these derashot as asmakhtot (secondary references which do not generate halakhot, but which the Rabanan employed to lend credibility to their takanot), the gemara appears to present them as actual derashot.
Rashi (2a) indeed identifies bedika as a means of circumventing bal yeira'eh. He does not, however, reconcile this position with the aforementioned gemara (4b) which allows bitul as a sufficient solution for bal yeira'eh. Two directions are adopted in amplifying Rashi's position in light of that gemara. The Kolbo cites a position - which some actually attribute to the Rambam - that bitul is ineffective upon known or visible chametz. Bitul, as a mechanism, is effective only with regard to chametz which is untraceable. Obviously, this would depend highly on our definition of bitul. But once we take this assumption, we might suggest a complementary role for bedika. Indeed, bitul would solve the problem of bal yeira'eh for some forms of chametz - the chametz which is unseen or inaccessible. However, bedika is necessary to attend to the chametz which bitul cannot address - the 'chametz yadua,' which simple bitul will not resolve.
Though this concept has interesting logical appeal, it is questionable in light of most gemarot, which discuss bitul in an unqualified manner. One gemara (6b) indeed might suggest a distinction between known and unknown chametz, but most Rishonim did not articulate such a distinction. According to most, the resolution to Rashi's position lies elsewhere.
One approach suggests that Rashi views bedika as a de-oraita requirement independent of bal yeira'eh. Beyond avoiding possession of chametz, there might also be an independent obligation to purge chametz. In fact, a famous inquiry of the Minchat Chinukh surrounds a person who does not own chametz when Erev Pesach nears. Does he have an obligation to actively acquire chametz to ensure fulfillment of a potentially independent mitzva known as 'tashbitu' ("Akh ba-yom ha-rishon tashbitu se'or mi-bateikhem" - Shemot 12:15)? Rashi might have required bedika even though bitul clearly and convincingly dispenses with bal yeira'eh, because bedika is still necessary towards the fulfillment of tashbitu. Though this idea has great logical merit, is certainly does not accord with the simple reading of Rashi, which implies that bedika is vital in solving bal yeira'eh proper (rather than an independent mitzva of tashbitu).
The most renowned solution to Rashi is suggested by the Ran (though traces of this approach already exist in a sefer known as Chidushei Rabenu David, authored by a talmid of the Ramban). Rashi claims that the Torah allows two independent and self-sufficient methods of solving bal yeira'eh: either bitul or bedika. The gemara which had proposed bitul as sufficient for bal yeira'eh was merely asserting it as one possible solution. But besides bitul, bedika also solves bal yeira'eh. Although the Torah allows one to adopt either method to avoid bal yeira'eh, the Rabanan demanded the performance of each. Rashi never suggested that bedika is necessary for bal yeira'eh - only that it was sufficient.
Interestingly enough, the Ran's position raises a provocative question: how can bedika alone fully address bal yeira'eh? Bitul, as a formal declaration, is all encompassing. It attributes a status to all chametz, seen or unseen. Bedika, by contrast, will only purge known or discovered chametz; it will neglect unfound chametz. How, then, could Rashi propose the partial solution of bedika as a self-sufficient means of avoiding the violation of bal yeira'eh? This question can be answered only by taking a closer look at the nature of bal yeira'eh – a topic to be covered iy"H in upcoming shiurim.