Although it wasn't coined until the 17th century, the word "nostalgia" has Greek roots. It's made up of the words nóstos, meaning "return home," and álgos, or "longing." It's these two components that make up Boym's two nostalgia types: restorative and reflective.

Restorative nostalgia deals with the "return home" portion, making you want to reconstruct and relive the way things were in the past. Reflective nostalgia centers on longing, letting you simmer in those wistful and yearning feelings while accepting that the past is the past. As Boym writes, "While restorative nostalgia returns and rebuilds one homeland with paranoic determination, reflective nostalgia fears return with the same passion."

For example, high school is a common trigger of nostalgia for many people. If you were to listen to an old mix CD from senior year, you might ruminate on the worries and hopes for the future you had as a teenager and marvel at how different life turned out to be. That amused acceptance of the contrast between past and present is a cornerstone of reflective nostalgia. On the contrary, if that mix CD stirred something else in you, making you feel as though life was better when you lived in your hometown, when you were with your high school sweetheart, or when you didn't have to deal with all the complexities of your chosen career, it might make you take action to change your life. That's restorative nostalgia, and it's the reason people do everything from calling old exes to reinstituting conservative religious governments.

Unfortunately, the past that restorative nostalgia urges you to recreate isn't real. You likely remember the good times out of context — in the high school example, you probably felt secure and accepted at home because you lived with your parents, and it's easy to forget the chores, curfews, and family arguments that came with that. Attempting to recreate your past can make you face some unpleasant realities.

The good news is that whether nostalgia is reflective or restorative — or "good" and "bad," as literature professor Hal McDonald puts it — has nothing to do with the memories themselves, and everything to do with your reaction to them. "The difference between 'good' nostalgia and 'bad' nostalgia," McDonald writes, "... has far less to do with the actual content of our remembered autobiographical past, than with our expectations about what those memories can do for us. It is not the past itself, but rather our attitude toward the past, that makes all the difference." When you're struck by a nostalgic memory, recognize that you probably remember it out of context, and try to be content with the feeling it gives you, not the way things could be.

For more information on nostalgia, check out "Nostalgia: A Psychological Resource (Essays in Social Psychology)" by Clay Routledge. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.