When it comes to drinking on Purim, the Talmud clearly understood what the scroll of Esther (the Megillah) was all about. In practically every chapter of the Megillah, someone is imbibing heavily at a drinking party. And the scroll concludes with Mordecai's instruction to the entire Jewish people to celebrate these days as "yemei mishteh v'simchah, days of drinking and rejoicing" (Esther 9:22).
An ambiguous law like that, however, would not be left unqualified by the rabbis. On Passover, precise amounts are defined so that one may fulfill the obligations of eating matzah and drinking the four cups of wine. So one might expect that the rabbis would define "days of drinking" in terms of the volume of wine or the number of hours one would be obligated to drink.
The rabbis of the Talmud paid close attention to the nature of the obligation. On Passover, the four cups of wine are for joy and for sanctification, but they also have symbolic associations with the expressions that God used for Israel's redemption. On Purim, however, the wine (or liquor) is not symbolic. It is functional. Consequently, the nature of the obligation is not defined by volume, but rather, by the effect upon the drinker.
How Drunk Is Drunk?
"Rava said: It is one's duty levasumei, to make oneself fragrant [with wine] on Purim until one cannot tell the difference between 'arur Haman' (cursed be Haman) and 'barukh Mordekhai' (blessed be Mordecai)" (Babylonian Talmud, Megillah 7b).