Much of this heavy taxation is a result of joint filing of income tax returns, producing the so-called marriage penalty.

But joint filing means that the family's second income, added on to the main one, is taxed at the couple's highest marginal tax rate.

In 1948, Congress responded by changing the law to allow joint filing, widening tax brackets enough that most married couples paid less than if they were single.

The Justice Department opposed the joint filing, saying the federal marriage law forbade it.

The joint liability rule is often justified as the flip side of a significant benefit that results from joint filing.

A joint filing by eighteen top media companies and trade associations puts the matter even more bluntly.

There is no joint filing.

It came out of administrative need: in a joint filing, the I.R.S. could not determine whose income was whose.

On the other hand, some taxpayers may benefit from joint filing.

The Cleveland-based Hyatt Legal Services, for example, charges $395 for an individual filer and $495 for joint filings in most of its offices.