With Republicans squabbling over whom to blame for the congressional page scandal, it's easy to forget that we've already identified the real culprit. I'm referring, of course, to alcohol.

When he resigned from the House, Mark Foley said he was entering treatment for "alcoholism and related behavioral problems," the latter including his online flirtation with teenage boys. His lawyer said the Florida Republican had written the sexually charged messages that got him into trouble while under the influence.

Alcoholic impairment may be the world's oldest excuse. It was the reason Noah cavorted naked in his tent, the reason Lot slept with his daughters, the reason (some say) Aaron's sons, Nadav and Avihu, brought "strange fire" into the Tabernacle.

The defense does not always work; Nadav and Avihu, for instance, were immediately consumed by divine fire. But it must work often enough for people to keep trotting it out after all these years, and why it does is a bit of a puzzle.

Foley seems eager to be known as a drunk as well as a pervert, pressing his case in the face of skepticism from associates who never noticed he had a drinking problem, who can't even remember seeing him with a drink at any of the Washington receptions he attended during more than a decade in office. And since one of Foley's incriminating instant message exchanges occurred during a House vote, he wants us to believe he was passing judgment on legislation while he was plastered.

Picturing Foley staggering into the House Chamber to cast a vote is supposed to make us think better of him. If he's an alcoholic, suffering from a disease that makes him incapable of drinking moderately, he is not fully responsible for his behavior. In those online exchanges with pages, it was his disease talking, not him.

Even Alcoholics Anonymous, the group that has done the most to promote the idea that habitual drunkenness is an illness, does not go quite that far. For one thing, people who know they have difficulty drinking responsibly can be held accountable for drinking to begin with. And while A.A. members have to acknowledge they are "powerless over alcohol" and submit themselves to God, they also have to accept responsibility for their actions and make amends to people they've wronged.

Even if some people are predisposed to drink heavily, that tendency does not explain how they act when they drink. Does anyone really believe that alcohol made Mel Gibson temporarily anti-Semitic, causing him to rail against the Jews when he was pulled over in Malibu for drunk driving? Or that Bob Ney, the Republican congressman from Ohio who mentioned "a dependence on alcohol" when he pleaded guilty to corruption charges, was driven by demon rum to accept lobbyists' goodies in exchange for official favors?

There is another way of understanding such cases, reflected in the aphorism "in vino veritas." According to this theory, alcohol reveals the true you.

But as the psychologist Craig MacAndrew and the anthropologist Robert Edgerton observed in their classic 1969 study of the subject, that cannot be the whole story. "With alcohol inside us," they noted, "our comportment may change in any of a wondrously profuse variety of ways ... How can the conventional understanding of alcohol qua disinhibitor possibly accommodate the fact that even within our own culture people who have made their bodies alcoholled differ so drastically both within and among themselves in their subsequent doings?"

Looking at differences in "drunken comportment" across settings, MacAndrew and Edgerton concluded that context plays a crucial role in determining how people behave when they drink. In particular, cultural expectations -- "what their society makes of and imparts to them concerning the state of drunkenness" -- can be the difference between violence and peace, surliness and sociability, loud lust and quiet contemplation. If we expect drinking to cause bad behavior, we help make it so.