Nostalgia was once considered an illness. Seventeenth century doctors used the word for the homesickness of soldiers far from home, and treated it as a disorder. Today psychologists see it differently. Research suggests that recalling fond memories of the past can raise mood, strengthen a sense of connection to other people and give life a feeling of continuity, especially in times of loneliness or change.
Nostalgia is not always benign. It can idealise a past that was harder than memory suggests, and it can be used in politics and advertising to sell the promise of a return to better times. Because memory edits experience, often keeping the good and blurring the bad, nostalgic longing may be directed at a past that never quite existed.
The distinction psychologists draw is between nostalgia that connects the past to the present and nostalgia that rejects the present in favour of the past. The first can help people cope with change; the second can make change harder to accept. Nostalgia, like many emotions, is useful when it informs the present rather than replacing it.