In theory, practice is the same as theory. In practice, it differs.

Ryan Avent speculates that the reason that Americans are opposed to a carbon tax, despite their avowal of support for action on global warming, is that they don't understand how the tax works very well.

I'd say they understand it all too well: a tax will make it more expensive for them to drive, forcing them to do less of it. If they didn't like driving right now, they wouldn't be doing so much of it.

This is true of a lot of policy plans for which advocates claim a groundswell of mass support: people support them in abstract, but in actual particulars, they are against them. People support universal healthcare--until the majority who are perfectly satisfied with their health care right now hear the details of the plans, and the taxes required to pay for the plans. People like wars, but not the part where we spend a lot of money and soldiers die. People think we should do something about the environment--but only as long as it doesn't involve driving less, or buying smaller, more fuel efficient vehicles and homes, or giving up the long-distance plane flight to Disneyworld, or . . . well, when you come right down to it, what Americans have so far proven willing to do is buy biodegradeable cleaning products once a year, and waste a lot of carbon dioxide talking about how the government should do something.