TAX WHAT YOU DON'T WANT, NOT WHAT YOU DO WANT:

Since the last reduction in United States corporate tax rates, in 1986, other nations have reduced their own business rates; corporations complain this is putting them at a sharp competitive disadvantage. In reality, though, few companies pay the official rate.

Many pay at a much lower effective rate, taking advantage of numerous tax breaks and loopholes and using aggressive tax strategies to shift profits to more generous tax territories abroad. Among the companies benefiting from lower effective rates is General Electric, which has paid total corporate taxes -- federal, state, local and foreign -- equal to 17.9 percent of its cumulative $81 billion in earnings over the last five years, according to an analysis by S&P Capital IQ.

FedEx paid 20.1 percent, Amazon.com 6.6 percent and Ford Motor 4.2 percent. G.E. said its tax rate was unusually low over this period because it had big losses during the financial crisis. FedEx said it took advantage of temporary incentives to make new investments.

Congress, under relentless pressure from business interests, has allowed corporate taxes to dwindle as a source of revenue. In 2012, they amounted to about 1.6 percent of gross domestic product, half the level collected in 1970. By comparison, the individual income tax generated 7.3 percent of G.D.P. last year.

Many industrialized countries collect more than that percentage, although they, too, have to contend with a competitive globalized world where multinational companies can shift profits beyond the reach of local tax authorities.

"Income is increasingly difficult to nail down," said Aswath Damodaran, a finance professor at New York University. "It is like nailing jelly to the wall. And the problem is only going to get worse rather than better."

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