^ 11.There are three levels of intoxication: tipsy, drunk, and as drunk as Lot. 1) An tipsy person is one who drinks wine until he feels somewhat happy and disoriented, but is still capable of standing respectfully before a king. Such a person may not recite the Amida until the effects of the wine dissipate, but if he nonetheless prays, his prayer is valid. 2) A drunk person is one who drinks so much that he cannot stand before a king because he is incapable of acting respectfully. If he recites the Amida, he does not discharge his obligation, because his prayer is an abomination. Nevertheless, he may recite Birkhot Ha-nehenin (berakhot recited upon deriving pleasure from something) even in his state of drunkenness. 3) A person who is as drunk as Lot is one who drinks so much that he does not know what is happening to him. He is like a shoteh (a mentally impaired person), who is exempt from all mitzvot. See Peninei Halakha: Prayer 5:11.
We can now apply these levels to the mitzva of drinking on Purim. Rif and Rosh cite Rava’s statement that "a person is obligated to get drunk (livesumei) on Purim until he does not know…" implying that they understand the mitzva according to its simple meaning. The Aramaic word livesumei means to get drunk, as Rashi explains (Megilla 7b). Apparently, this relates to the second category mentioned above – that of a drunk person. In contrast, a person who is as drunk as Lot cannot discern anything, let alone the difference between "Cursed is Haman" and "Blessed is Mordechai." However, even within the category of a drunk person, there are different levels: 1) one who cannot stand before a king and speak properly; 2) "until he does not know," which is as I explained in the main text: He cannot discern details, but instead shows an indiscriminate perspective. As the Sages state, "One who puts his eye on his cup (i.e., is drunk), the whole world appears to him like a plain" (Yoma 75a). Such a person forgets his troubles, and everything is for the good in his eyes – both "Cursed is Haman" and "Blessed is Mordechai." Such a drunk person is liable to disgrace himself. Many authorities maintain that the mitzva to get drunk on Purim refers to this level of drunkenness, and Taz and the Vilna Gaon seem to agree. Ĥakham Zvi and many other great scholars adopted this approach in practice. Raavya 2:564 states that it is a mitzva to get drunk "until he does not know," but one is not obligated to do so. Apparently, his reasoning is that it is possible to fulfill the mitzva of drinking without reaching this level of drunkenness. From the words of Rif and Rosh, however, it seems that it is obligatory. Even though the Talmud relates that Rabba slaughtered R. Zeira because he was so drunk, implying that it is bad to drink in excess, the fact that Rabba invited R. Zeira to join in his Purim feast again the next year and that R. Zeira was apprehensive about going implies that the mitzva is indeed to get drunk "until he does not know," in the literal sense (Eshkol, Pri Ĥadash).
MT, Laws of Megilla 2:15 states, "One should drink wine until he gets drunk and falls asleep in his drunkenness." This, in essence, is an intermediate opinion. On the one hand, one must reach the level of "until he does not know," but he should not do so while awake, because that would mean he is very drunk. Rather, he should fall asleep as a result of his drunkenness. Mahari Brin concurs with this opinion, and it is cited in Rema 695:2.
Others maintain that one does not need to get so drunk, because drunkenness is shameful and liable to bring one to commit serious transgressions. So states Orĥot Ĥayim. Similarly, Me’iri states: "We are not commanded to get drunk and degrade ourselves in the process of rejoicing, for the type of joy we are commanded to achieve is not one of debauchery and folly, but one of pleasure that leads to loving God and thanking Him for the miracles He performed on our behalf." Ha-ma’or states in the name of Rabbeinu Ephraim that the fact that the Gemara related the story of Rabba slaughtering R. Zeira implies that the halakha does not require us to drink "until he does not know." However, it is clear that even these opinions agree that one must drink enough to become tipsy to the point that it would be forbidden to pray. This is clearly indicated from the discussion concerning the timing of the meal, which the poskim determine should take place a significant amount of time before the time of prayer, since one may not pray immediately after the meal. Furthermore, it is a mitzva to drink more on Purim than one does on Yom Tov, since Purim is a day of mishteh. It is a mitzva to drink on Yom Tov in order to rejoice, and it seems that one must drink at least a revi’it measure (Torah Or 99:3). And since one becomes tipsy after drinking only a revi’it, it follows that on Purim one must drink until he nears the level of drunkenness.
Tosafot and Ran explain that one must drink enough to occasionally stumble on the words "Cursed is Haman and blessed is Mordechai." Abudraham explains that there was once a song that required the audience to respond accurately – sometimes "Cursed is Haman" and sometimes "Blessed is Mordechai"; people who were intoxicated would often get confused. Aguda and Rabbeinu Yeruĥam explain that the numerical value of both phrases is the same, and when people drink they find it hard to calculate the numbers. Nimukei Yosef explains that one must drink and joke around until he makes himself appear as if he does not know the difference between Haman and Mordechai. According to these opinions as well, the mitzva is to become tipsy, not drunk. They maintain that the halakha follows Rava, that one must drink "until he does not know," but that this does not mean getting totally drunk. Shlah and Responsa Rema Mi-Fano maintain a similar position. Upon examining these opinions, we find that the mitzva is to become tipsy or even slightly drunk. This fits with the opinion of Baĥ, which accepts the position of Rabbeinu Ephraim in practice, but states, "One should become tipsy or even drunk to the point that he cannot speak before a king, but he should retain his faculties." Yad Ephraim also is in this vein, but maintains that Rava’s statement was not rejected. Rather, he meant that one should get drunk until "he does not know," without actually reaching that extreme level of drunkenness ("ad ve-lo ad bi-khlal"). Sefat Emet and R. Yisrael Salanter also write along these lines, explaining that one must drink all day long, with the goal of being happy, but if he reaches the state of "he does not know," he becomes exempt from the mitzva of drinking and does not need to continue.