Law professor Nancy Polikoff, author of the important new book, Beyond (Straight and Gay) Marriage: Valuing All Families under the Law, left this comment on one of my previous blogs:

Last week, I blogged about a bus shelter poster campaign in Washington, DC. (www.beyondstraightandgaymarriage.blogspot.com) The posters have a bride and a groom and a statement. This "marriage promotion" campaign comes from a group that received almost $5 million in GOVERNMENT funding in 2006. (The group also supports abstinence-only sex education.) One of the posters reads: "Married people earn more money." Can you tell us what's wrong with that statement as an encouragement to marry?

I've looked into all sorts of claims about the joys and rewards that will be yours if only you wed - for example, that getting married makes you happier, healthier, sexier, lengthens your life, and saves your children from the doom that would befall them if they were raised by a single parent. When I assessed these vaunted benefits of getting married for my book, Singled Out, I found that just about all of them were myths. The supposed "evidence" in support of most of these claims is typically misrepresented, exaggerated, or just not there.

Here's the exception. The link between getting married and having more money really is there - and for all the wrong reasons. People who marry are rewarded with a treasure trove of economic goodies withheld from people who stay single.

Consider, for example, the issue of such prominence in the Democratic presidential campaign: health insurance. In many workplaces, married employees can include their spouse on their health plan at a reduced rate. Their single co-workers - who may have been doing the same job at the same level of competence for the same number of years - cannot include another adult (such as a sibling, parent, or close friend) on their plan. Analogously, no other workers can include those single people on their plans. That amounts to unequal compensation for the same work.

Same for Social Security. After married workers die, the benefits they earned go to their spouse. The same benefits earned by single workers go back into the system. Singles cannot give their benefits to other people who are important to them, nor can other workers leave their Social Security benefits to adults who are single.

It is not even necessary to look at benefits to find workplace discrimination against people who are single. A stack of studies has shown that married men are paid more than single men - even when the two are comparable in their seniority and accomplishments. (The references are in Singled Out.) In fact, in one study of identical male twins, the married twin was paid an average of 26% more than the single twin.

There is a supposed "penalty" for getting married that may well be the most notorious of them all. You may even have it on your mind around this time - the purported "marriage penalty." Just how bad is it? If a single person's taxable income were exactly the same as that of a married couple filing jointly, how much more would the married couple pay in federal taxes? It differs at different levels of income, but one part of the answer never changes: It is the single person who ALWAYS pays more. That's a singles penalty, not a marriage penalty.

Those who fret about the "marriage penalty" are not comparing married couples to single people. They are comparing two kinds of couples: those who are married, and those who pool their income but are not married. Under some conditions, the couples who marry do pay more in federal taxes than the couples who do not. Still, getting married more often results in a perk than a penalty.

Income taxes are just one of the domains in which the federal government favors people who get married. There are many other tax advantages and legal protections. In fact, as of 2004, there were 1,138 federal provisions in which marital status was a factor in the allocation of benefits, rights, and privileges. That's just the feds - states can pile on their rewards as well.

The marketplace is more generous to married people, too. Whenever people who are married pay less per person than people who are single, they are being subsidized by the single people who are paying full price. The list of examples begins with car insurance, club memberships, and travel packages; continues through restaurant coupons and grocery discounts for those who buy the jumbo sizes; and never ends.

Adults can access all of these legal benefits and protections and all of the economic perks simply by getting married. No child-rearing needs to be involved. In fact, married people can behave badly toward their spouse, dishonor their vows, move into a hotel room, and still remain recipients of the government's largesse.

Back to those posters that Professor Polikoff mentioned. "Married people earn more money," they claim. (The money is not really "earned," but never mind.) So why not get married for the money?

Remember that the posters are in bus shelters, not yacht clubs. The people who are targeted by the marriage-promotion campaigns are primarily those who are poor. Unwed mothers are of particular interest to the leaders of the marriage movement. So, "Is Marriage a Panacea?" That was the question posed by a study published in the journal Social Problems in 2003. The researchers found that unwed mothers from economically disadvantaged backgrounds who married did in fact, on the average, do better financially - but only if they stayed married. To quote the authors, "for women who marry, but later divorce, poverty rates exceed those of never-married women."

Now, finally, for the psychology. I'm no sappy romantic, but seriously - do you really want to marry for money?

Suppose you do. Ethics and values and fairness aside, would there be anything wrong with that?

Psychology students and fans may be familiar with a simple study from long ago, one that touched off decades of intriguing research. The participants in the study were children who loved playing with magic markers. Some of the kids (randomly assigned) were rewarded for doing what they already loved to do; the others were not. The rewarded children subsequently liked playing with the markers less than they had before! When the kids saw their drawing as something they did in order to get rewarded, their intrinsic motivation was undermined.

What if adults come to see the act of getting married as something to do in order to get more money? That's what the marriage-promotion posters seem, in a way, to be suggesting. Would the couples come to love one another less than if they had not been tempted by the promise of financial gains? Fortunately, scientists do not set ethics and values and fairness aside, so the relevant experimental research will never will be done. All we can do is guess. What do you think would be the consequences of marrying for money?