How "precommitment devices" will force you to lose weight, stop drinking, and not sleep with that jerk on a first date.

The evidence is all around us that Americans are struggling—and often failing—to uphold their preferred desires. Hardly anyone wants to be fat, after all, yet two-thirds of us are. A large proportion of smokers have tried to quit. Most procrastinators would prefer to escape their dilatory impulses but struggle to overcome their powerful wish to avoid work.

The problem is that short-term rewards are just so much more seductive than long-term goals. And besides, what's one little dessert, one more puff, or just a few more minutes at World of Warcraft when your thesis isn't due for another year? People often understand how weak they are in this way, which is why (for example) they support the Social Security system, a giant precommitment device whereby we subject ourselves to taxation in order to forestall destitution that we could easily prevent if only we could save for ourselves.

How can you use precommitment to keep yourself from giving in to unwanted desires? You're probably already doing so—for example, by asking your significant other, on the way to a restaurant, not to let you order dessert when you get there. Dan Ariely, that tireless student of human irrationality, has collected several interesting precommitment anecdotes from regular people, including one who placed her credit card in a container of water in the freezer, thereby requiring a cooling off—er, that is, warming up—period before use, and another who, before a date with a guy she knew she shouldn't sleep with, wore her "granniest" underwear—presumably to deter herself from disrobing. In this she was unwittingly following the advice of St. Jerome, who argued that the determined virgin, "by a deliberate squalor … makes haste to spoil her natural good looks." Jerome's friend Paula, who ran a convent near his monastery in Bethlehem, evidently took the same view of cleanliness and chastity, warning, "A clean body and a clean dress mean an unclean soul."

Most of us really ought to make more use of such techniques, as Dean Karlan and John Romalis did. The two economists each agreed to lose 38 pounds in six months or forfeit half his annual income to the other. They made a similar deal to keep the weight off afterward. This all worked well enough that Karlan later went on to found stickK.com, a Web site that allows you to provide a credit card number and make a legally binding agreement to do (or not do) a certain thing. If you fail—and you can appoint a referee to decide—then you forfeit the money, which the site will give to a friend or enemy you've chosen. (You can also choose a charity you like—or one you hate, such as the George W. Bush or Bill Clinton library, which might be even more motivating.)

As a libertarian-leaning Democrat, I've tried to think of ways the government might help us with precommitment. Some states and Canadian provinces already allow gamblers to bar themselves from casinos for a period of years. In British Columbia, some gamblers on the self-exclusion registry got in anyway and lost several hundred thousand dollars. They sued the province and the casinos for failing to do what Jenny Holzer said: "Protect me from what I want."

What if we took this kind of thing further? One possibility might be to let people sign up to pay extra taxes based on the change in their weight. Health costs are largely socialized anyway, and there is precedent in the private sector, where insurers setting term-life premiums often take account of smoking, cholesterol, and other factors that individuals can influence. Another idea would be to require a driver's license or other I.D. for the purchase of cigarettes or alcohol. The state would offer to emblazon these "NO TOBACCO," for example, until the next renewal, perhaps three years later. During that time stores couldn't sell you the stuff.

Modern life is a wonderful thing, rife with freedom and opportunity, but it comes with the problem of self-control. That's a nice problem, since I can't think of anyone else I'd want to be in charge. Yet most of us are probably kidding ourselves if we think willpower alone can do the job. Much better to make like Odysseus and face the music in safety.

Correction, Jan. 21, 2011: Thisarticle originally said the device from Progressive Insurance would rat you out for speeding. But while the device records your speed, it doesn't know where you are, and the company says it can't tell if you were violating any speed limit. Customers install the device only if they want to. (Return to the corrected sentence.)

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