THE word “cool” has been cool for a long time. Originally associated with temperature, by the 16th century the term had evolved to describe not just the atmosphere, but also an internal state of calm, almost icy composure. And by the late 1800s it began to signify style and hipness and some of the other meanings with which it is associated today. Now cool is used as a synonym for almost anything good. Music can be cool and restaurants can be cool. Every so often even a minivan seems cool.

But not all words and phrases persist. In the 1940s, dress snappy and someone might say you looked “spiffy.” In the 1950s, people might say you looked “swell.” These days, teenagers might say you’re “on fleek.” What was once “awesome” is now “dope.” Tell someone today that they look spiffy and people will think you’re caught in a time warp.

Language is constantly evolving. Certain words and phrases catch on and become popular while others die out and wither away. So what leads some phrases to become more successful than others? Why do some survive the test of time while others die out?

There’s no record of every time someone utters a certain word or phrase, so to study these questions, my colleague Ezgi Akpinar and I turned to the next best thing: books. For hundreds of years, of course, books have documented the words and phrases used to express different ideas. This includes everything from Shakespeare‘s sonnets to Jane Austen’s description of the landed gentry, and many thousands of works by unknown authors in between. Books provide a written record of culture, a constantly evolving collection of snapshots of what things were like across time and space.