According to Miral Fahmy of Reuters, researchers first put their subjects in sad or happy moods by having them watch movies or recall positive or negative memories. Then they conducted several different experiments. They found that people in bad moods were less likely to believe urban myths or rumors, and were also less likely to make decisions based on racial or religious prejudice. They were better at remembering events they'd seen, and better at persuasive writing. Study author Joseph Forgas wrote that a "mildly negative mood may actually promote a more concrete, accommodative and ultimately more successful communication style." He added, "positive mood is not universally desirable: people in negative mood are less prone to judgmental errors, are more resistant to eyewitness distortions and are better at producing high-quality, effective persuasive messages."
So despite the conventional wisdom that thinking positively will help us solve all of our problems, it seems that feeling sad can actually be productive — maybe there's a use for a bad mood after all. Negative feelings appeared to boost subjects' critical thinking skills, the kind of skills that come in handy when something bad happens to you. Being the victim of a crime would be a good example — if it puts you in a bad mood, you may actually remember the incident better, making it more likely that the police can catch the criminal. Perhaps bad moods, rather than being a relic of some less-evolved mental state, are actually adaptive, sharpening our cognitive faculties when we need them most. As Forgas says, "our research suggests that sadness ... promotes information processing strategies best suited to dealing with more demanding situations."
Of course, the research raises questions. Were the good or bad moods induced by scientists really similar to feelings subjects would experience on their own? And how bad does a bad mood have to be before it stops being a help and starts being a hindrance? Clinical depression might actually reduce cognitive ability, and it seems possible that a certain intensity or duration of negative feelings could impair judgment rather than boosting it. Still, it's intriguing and in a way reassuring to hear that our bad moods may be doing something for us — perhaps instead of fighting against them, we should learn to use them.