Alex Bentley, a professor at the University of Bristol, researched the use of emotional language over history.

NPR’s Alix Spiegel reported on a really cool project this week: essentially on a whim, a team of researchers in England started charting the frequency of words that carry emotional content in 20th century literature, with results that show distinct correlations with major world events.

Alex Bentley, the anthropologist at the University of Bristol who led the team, told NPR that they started their research without any sense of what they would find. “We were just curious,” he said, “We really expected the use of emotion words to be constant through time.” They published their findings in the science journal PLOS ONE, including charts like the one below that show some clear shifts in mood at some key moments:

This graph shows the frequency of joyful language throughout the 20th century.
Alberto Acerbi, Vasileios Lampos, Philip Garnett, R. Alexander Bentley/PLOS ONE

Perhaps not surprisingly, the 1920s show the “highest peak of joy-related words,” with a sharp decline in the late 1930s and 40s. The lowest point, in 1941, marks the US’s entry into World War II. And as Bentley points out, this data came from a vast variety of books, not just novels embracing the opulence of the Jazz Age or gloomy wartime poetry about missing limbs; many of the books surveyed were manuals or other technical books, so it seems like the emotion of the times was pervasive enough to be “creeping in,” as Bentley puts it, to areas of writing where you might not expect it.

The method behind the research was fairly simple: using a Google database of digitized books, Bentley and the other researchers conducted a search for words that connote different emotions. All told, there were 224 synonyms for joy, 146 for anger, 115 for sadness, 92 for fear, 41 for surprise, and 30 for disgust. Psychologist James Pennebaker expressed excitement over this kind of language analysis, which has the potential to help us observe the mood of a culture more objectively, because “using these language samples, we are able to peg how people are feeling over time. That’s what I love about it as a historical marker, so we can get a sense of how groups of people—or entire cultures—might have felt 10 years ago, or 100 years ago.”

The other finding, perhaps surprising in this age of oversharing, is that use of emotional language has been in decline, with the exception of fear synonyms, which have been on the rise since the 1980s. (I have to think that if this research expanded to the written word on the Internet, there would be a sharp uptick in disgust synonyms as well). Bentley says he doesn’t have an explanation, because like any good nerd, he was just happy to share the data—or, presumably, cause a panic over the possibility that we’re all becoming cynical, unfeeling robots.

This graph shows the decrease in emotion-related words over the past century.