Mitt Romney’s tax returns have stirred up a lot of interest recently, because he refuses to let the public see more than two years’ worth.

Unless you believe the unsupported charge by Senate Majority Leader Harry Reid, a Nevada Democrat, that Romney’s returns would reveal that he paid no taxes, we probably already know much about his tax situation.

What we can learn from Romney’s tax return is proof of what the well-known author F. Scott Fitzgerald once wrote: “Let me tell you about the very rich. They are different from you and me.”

The very rich are different because they pay less of their income in taxes than do most average wage earners.

It is probably perfectly legal. High-income people are able to take advantage of provisions of the tax law that are simply not usable by most average taxpayers.

Why? In part, their tax advantages stem from their ability to spend on lobbyists who try to influence what tax laws are adopted. Also, some members of Congress believe that investments by the wealthy create jobs, so they should be encouraged to put their money to work rather than paying it to the government.

Romney took advantage of only a few of the possible ways of cutting his tax liability. A vast majority of people might readily conclude that there is no chance they could use them.

It starts with capital gains. If you make an investment and later sell it, any gain that you make on the value of the investment is taxed at 15 percent. That is much less than the 35 percent you might pay, if the gain were taxed like wages.

Any capital loss can be used to cancel gains.

The purpose of this federal tax break is to encourage people to invest, because they get to keep more of the profit. It is unclear if investing is really affected by this tax break.

Some states, including Maine, do not offer such a tax break. Investment gains are taxed at the same rates as wages.

For certain large investments, the taxpayer is allowed to treat income that is really a payment for services as if it were a capital gain, even after the investment itself has been repaid to the investor. It’s called “carried interest.”

Much of Romney’s $22.8 million income in 2011 got that special tax treatment. That may have saved him an added $2 million in taxes. He paid $3.2 million.

Another way to reduce taxes is to make large charitable contributions. When they are deducted from income, the remaining income may be taxed at a lower rate.

Often wealthier taxpayers, including Romney, make some of their charitable gifts in the form of corporate stock. They get a deduction for the current value of the stock, even if they originally bought it for much less.

In 2011, Romney made $4 million in gifts, paying more to charity than to the tax collector, which few can do. Most of his contributions went to the Mormon Church of which he is a member.

More Romney tax returns would most likely reveal that he had used the same tax preferences in earlier years. That’s why we probably already know much about his tax situation without seeing his returns.

The income tax system is supposed to be “progressive,” meaning that lower income people pay at lower rates than the wealthy. To some extent that is true, because many lower income people pay no income tax. For example, a family of four with income less than $26,400 pays no federal income tax.

However, middle-income taxpayers, who get little if any capital gains breaks or cannot make large charitable gifts, are likely to pay at a higher rate than people like Romney.

When Congress gets back to cutting the federal deficit, it will have to deal with the expiring Bush-era tax cuts. And the main issue will be how to treat the wealthiest taxpayers.

One way to increase federal revenues, with the added money used to reduce the deficit, would be to end the tax cuts for the wealthiest.

Or some of the preferences, like carries interest, that can be used only by the most wealthy could be eliminated.

Yet another way of raising revenues through the tax code could be to allow all breaks to continue but to put a dollar cap on their use.

The lesson we need to learn from Romney is not that he is rich, but that he legitimately benefits from a tax system that needs to be fixed. He could probably help himself at lot politically if he advocated some reforms affecting his own taxes.