The Talmud - which normally presents a particularly severe view of intemperence - features a strange statement about Purim: "You should drink until you don't know (ad lo yada) the difference between 'Cursed in Haman, Blessed is Mordechai.'"

In Judaism, alcohol is a sober pleasure (pardon the pun). We appreciate the fact that it gladdens the heart, and include it in all our festive occasions. What would Pesach be without the four cups? Or Shabbat without kiddush? Every holiday, and personal occasions like weddings and Britot (circumcisions) include a kiddush (glass of wine). Yet to get drunk is "not Jewish" at all, and is condemned strongly by the Sages.

What gives with Purim?
Throughout the Purim story, wine is a key factor in the drama. It's Achashverosh's drunken demand that Vashti show off that brings her downfall and clears the way for Esther to become queen. It's again a wine feast that Esther invites Haman and the king to - which results in Haman's downfall.

In the great party thrown by Achashverosh in the beginning of the Megilla, drinking played a key role. The Sages say that because the Jewish community attended and enjoyed this bacchanalian feast, God sent a punishment in the form of Haman. The Jews' subsequent teshuva (repentence) corrected this mistake, and now we can feast with the correct attitude - rather than reveling in a lustful orgy of eating and drinking, we eat and drink to praise God for our salvation.

Opinions differ as to whether the Talmidic dictum above really means drink to incoherence. The sources stress that Purim is a holiday to bring out what's hidden within - but this should only be undertaken by those whose insides bear inspection - As long as drinking brings a person to simcha (happiness) and to sweeten their behavior, it's positive. If drinking brings out aggression or offensiveness, it's no good. The injunction to drink doesn't apply.