How do you get people in a democratic society to change their way of life? The theme has come up a lot at gatherings of climate scientists and environmentalists I've attended, where the answers fall on a continuum between "persuade them" and "force them." That's not a distinction between good guys and bad. Persuasion isn't inherently democratic, because it can be based on lies and distortions. Mandates aren't inherently tyrannical, if they're enacted by fairly-elected legislatures.

What really separates these two philosophies is the place they want to see change: Is it within people, or among people? Do you want people to make the better turns on the road of life, or wall off the bad ones so that they can't?

One point in favor of individual change is that it sounds kinder and more democratic: around the world today, for example, millions of people lucky enough to have electricity have been unplugging from the grid for "Earth Hour," to illustrate the "small changes from all of us at home" that, writes the World Wildlife Fund's David Nussbaum will be required to avert catastrophic climate change. Candlelit dinners and family storytelling have a warm aura not found in rulebooks, courtrooms, and jail cells.

On the other hand, as a paper in this month's Journal of Personality and Social Psychology illustrates, there's a drawback to personal behavior as a tool of social change: The choices people make in their personal lives are never just about the objects or actions in play. They're also about how we see ourselves, and how we imagine others see us. Like a medieval allegory, where the unicorn is both a unicorn and a symbol of Devotion, a decision to buy an iPhone is a double story: The phone is a phone, and also a symbol of your place in society. The same goes for choices in beer, shoes, cars, hobbies and habits—including whether to participate in "Earth Hour."

Allegory is hard to sell to modern readers. We want the unicorn to be all unicorny, and not do strange things that are required because he is also a symbol of Devotion. Similarly, environmentalists like to believe that "green" behavior is about an enlightened appreciation of the facts; they hate to think that "green" deeds can be driven by that other level of consciousness, where they represent status and self-image. And those anxieties are well-founded. If "green" choices are motivated by self-image and social emotions, that means those decisions can't be relied upon. "Green," though always good for the planet, will eventually no longer represent social "cool."

The Journal paper shows that this problem is real. The authors—Vladas Griskevicius, Joshua M. Tybur, and Bram Van den Bergh— asked 168 college students to pick between a range of products, some of which were noticeably "greener" than others. Before they did so, though, the students were divided into groups. One read a story that focussed their attention on matters of social status.

The students who'd been primed to think about status were far more likely to choose the eco-friendly products. And, as this account points out, a later experiment showed that the status-aware students were less likely to prefer green if they were shopping online (where no one could see them) than in a brick-and-mortar store. The paper also notes that, among the status-aware students, the desirability of green products dropped if those products weren't more expensive than alternatives.(The full paper, in pdf form, is here.)

There's a practical conclusion to be drawn from this: We shouldn't necessarily expect eco-friendly products to take off once they become less expensive and more common. For those for whom eco-awareness is a badge of elite status, the appearance of green bulbs at Wal-Mart makes those bulbs less desirable.

But I think the deeper lesson is this: we can't and shouldn't expect environmental change to take place within people's minds and hearts. People's minds and hearts aren't that reliable, and their motivations are primarily those that evolution bequeathed us: Impressing ourselves, and other people, with representations of identity. The allegorical nature of personal choice is inescapable.

Granted, all democracies depend on a mix of individual motivation and social rules (we pay taxes both because it is the law and because we want to feel virtuous). So this is not an either/or choice. But I think our knowledge of the human mind is sound enough, now, to tell environmentalists that they're better off trying to change laws rather than people. "Earth Hour" is "in" this year. By 2013, it may be "out." But a law making it impossible to buy gadgets that run on standby mode? That's something you can count on.