Beware Social Nostalgia - NYTimes.com AS a historian, I've spent much of my career warning people about the dangers of nostalgia. But as a mother, watching my son graduate from medical school on Thursday, I have been awash in nostalgia all week. In personal life, the warm glow of nostalgia amplifies good memories and minimizes bad ones about experiences and relationships, encouraging us to revisit and renew our ties with friends and family. It always involves a little harmless self-deception, like forgetting the pain of childbirth. In society at large, however, nostalgia can distort our understanding of the world in dangerous ways, making us needlessly negative about our current situation. Nineteenth-century Americans were extremely worried, the historian Susan Matt points out, about the incidence of nostalgia, which was the term used to describe homesickness in those days. According to physicians of the era, acute nostalgia led to "mental dejection," "cerebral derangement" and sometimes even death. The only known cure was for the afflicted individual to go home, and if that wasn't possible, the sufferer was seriously out of luck. Such was the quandary facing soldiers during the Civil War, when going home constituted desertion. Doctors diagnosed 5,000 clinical cases of nostalgia in Union soldiers and determined that 74 men had died from the affliction. To contain the epidemic, military officials prohibited Army bands from playing "Home, Sweet Home," while ministers and officers avoided references in sermons or speeches that might touch off a new outbreak. When present-day nostalgia involves homesickness for a period of time or a way of life that is gone for good, it's time to follow the example of 19th century military commanders and stop fostering longings for the past that produce "mental dejection" about our prospects for the future. There's nothing wrong with celebrating the good things in our past. But memories, like witnesses, do not always tell the truth, the whole truth, and nothing but the truth. We need to cross-examine them, recognizing and accepting the inconsistencies and gaps in those that make us proud and happy as well as those that cause us pain. In my work as a historian and in my relationships as a friend, teacher, wife and mother, I have come to think that the most useful way to understand the past, and make it work for you, is to look at the trade-offs and contradictions that, however deeply buried, can be uncovered in every memory, good or bad. The psychologist John Snarey has studied men who had very difficult childhoods because of their fathers" poor parenting. Some of these men replicated the same problems in their relationships with their own children. But others were able to use the memory of what their fathers did wrong to chart a different course in their own parenting. What separated the two groups was that the successful ones neither idealized their own fathers nor focused on their shortcomings. Rather, they placed their fathers" failures in context, turning their anger "into a sense of sadness for and understanding of the conditions under which their own fathers had functioned." Their unhappy memories became a guide for avoiding bad behavior rather than an excuse for it. Happy memories also need to be put in context. I have interviewed many white people who have fond memories of their lives in the 1950s and early 1960s. The ones who never cross-examined those memories to get at the complexities were the ones most hostile to the civil rights and the women's movements, which they saw as destroying the harmonious world they remembered. But others could see that their own good experiences were in some ways dependent on unjust social arrangements, or on bad experiences for others. Some white people recognized that their happy memories of childhood included a black housekeeper who was always available to them because she couldn't be available to her children. Some sons and daughters realized that their idyllic summers at the beach happened only because their mother had given up something else she had very much wanted to do. Some husbands - and those were among the most touching interviews I did - came to understand that the homes they regarded as personal oases seemed more like prisons to their wives. They were then able to support a wife or daughter who chose a course that took a man out of his comfort zone. These people didn't repudiate, regret or feel guilty about their good memories. But because they also dug for the exceptions and sacrifices that lurked behind their one-dimensional view of the past, they were able to adapt to change. Both as individuals and as a society, we must learn to view the past in three dimensions before we can move into the fourth dimension of the future. Stephanie Coontz, a guest columnist, teaches at The Evergreen State College in Olympia, Wash.