The rising usage of swear words in literature suggests that American society is becoming increasingly individualistic

Comedian George Carlin's 1972 routine "the seven words you can never say on television" underlined his generation's rejection of the niceties and constraints of post-war American society. Seeing how the use of these swear words has changed over time captures the evolving American psyche, according to a new study by San Diego State University psychology professor Jean M. Twenge.

"The increases in swear words in books is part of a larger cultural trend toward individualism and free expression," said Twenge, also the author of the book, Generation Me.

For the study, Twenge, along with SDSU graduate student Hannah VanLandingham and University of Georgia psychologist W. Keith Campbell, analyzed the textual content from tens of thousands of books published between 1950 and 2008, and that have been catalogued by the Google Books database. Within this corpus, they searched for instances of Carlin's seven notorious words (which we won't print here but are noted in the study, or can be easily found online).

They found a steadily rising trend of those words appearing in the books, the team reports in the journal SAGE Open. In total, American authors used the seven risqué words 28 times more often in the mid-2000s than the early 1950s, the study notes.

"Forty-five years after George Carlin's routine, you can say those words on television—and in books," Twenge said.

The findings suggest that these words have become much less taboo over time, she said. One interpretation is that people today value free expression more than they did several decades ago. That dovetails with previous research which has found that American society is becoming increasingly individualistic. That characteristic is especially prominent in young people, Twenge said.

"Millennials have a 'come as you are' philosophy, and this study shows one of the ways they got it: The culture has shifted toward more free self-expression," she said.