Most of us would agree that discrimination based on social categories is wrong. Instead, we think we ought to judge each individual on his or her own merits. We repudiate "whites only" drinking fountains or the unwillingness to hire someone simply because he or she is Latino or LDS. But we often don't live up to our values. Many people, in fact, unwittingly discriminate against others even though they think it is unwise or unjust.

Research in social psychology shows we are less aware of discrimination today, in part because it has taken new and more subtle forms. We no longer have explicit and bigoted policies that exclude blacks from our workplaces. Instead, black job applicants are interviewed in subtly different ways so they are set up to fail. Subtle discrimination can be just as pernicious as earlier overt forms because it is often hidden from those who engage in it. And being more easily denied, it is perhaps even more persistent.

Discrimination begins with stereotyping — attributing to each member of a group the characteristics thought to be typical of that group. When we stereotype, we fail to attend to the variation among members within each group. Overestimating the differences between ourselves and other people decreases our ability to form social bonds, experience empathy and to understand others — all of which lead to inadvertent discrimination. Worse, these mistakes are more likely to be made by those who have power, those who are experiencing strong negative emotions like fear or stress and by those who are not accountable for their actions. Sometimes stereotyping can even become ugly bigotry and hate.

Not only do we misunderstand the causes of discrimination, we often misunderstand its consequences. Subtle discrimination causes harm to its individual victims, but discrimination also has negative effects on those who discriminate.

Discrimination limits our openness to new experiences, our ability to develop new concepts and skills and our competitiveness. Imagine a law firm that decided not to hire women because the managing partners believed a woman's place was at home. Such a decision in 1960 was discriminatory. In 1980, it was discriminatory and illegal. Today, it is discriminatory, illegal and stupid. Nearly half of all current law students are women. Any firm that refuses to hire women loses out on half the pool of talented young attorneys. Perhaps the United States would be safer today if, over the last decade, the military had not dismissed tens of thousands of gay soldiers — including dozens of Arabic and Farsi linguists.