A quick follow-up to my post on the bizarre tax incentives for hybrid vehicles.

As fate would have it, David Leonhardt at the New York Times looks at this scheme and confirms the explanation made by many commenters in the last thread -- the goal of the tax credit is to help the domestic auto industry, not energy conservation:

The first thing to understand about the hybrid tax credit is that it was never really intended to reduce oil imports from the Middle East or slow the effects of global warming. The credit was created to prop up Detroit while giving conservation a nod.

Last summer, when Congress was completing an energy bill, Toyota's and Honda's hybrids were already winning people over in the marketplace, and it was clear that any tax credit would go overwhelmingly to buyers of Japanese cars. So members of Congress, with help from Detroit's lobbyists, came up with an ingenious solution. They created a cap, a maximum number of hybrids that any single manufacturer could sell — 60,000 — before a clock started ticking, causing the credits for that carmaker to begin disappearing two quarters later.

The idea, Mark Kemmer, a G.M. lobbyist, told Automotive News, was to keep any one company from getting "a runaway benefit."

Toyota hit the 60,000 mark last month, less than five months after the Jan. 1 start of the program, and the credits for its hybrid buyers will be cut in half on Oct. 1. (Because there are waiting lists for the Prius and Camry Hybrid, people who buy one in August or September may get their car after Oct. 1.) On April 1, 2007, the credits will be cut in half again. On Oct. 1, 2007, they will vanish. Honda, for its part, will probably hit the cap next year.

And the Big Three? Combined, they have sold fewer than 15,000 eligible vehicles so far, all by Ford, largely because their hybrids have not impressed buyers. Rather than building highly efficient hybrids like the Prius, Detroit has tinkered with gas guzzlers like the Chevrolet Silverado, adding hybrid technology to them so that they get slightly better mileage.

Come next year, then, the government will pay you to buy a Silverado hybrid (which gets about 16 miles per gallon) or a Ford Escape Hybrid (which gets about 26, according to Consumer Reports), but not a Prius (44) or a nonhybrid Corolla (29).

Much of the law has a kind of internal coherence. The common law, especially, is a kind of organic effort to rationally work out social ordering. Federal statutes are often broad efforts to impelement a basic policy objective -- sometimes successfully, sometimes not. Because the law "makes sense" much of the time, one can usually infer the "purpose" of a law from its provisions.

When I took tax in law school, I learned exactly one thing: Do not spend any time trying to make sense of tax law. It has no coherence. It is pure sausage. Special interests get the most they can get away with, and if what they fail to get often does not reflect any argument they lost but instead reflects the limits of their power weighed against other budgetary considerations.