The rise and fall of rationality in language

The surge of post-truth political argumentation suggests that we are living in a special historical period when it comes to the balance between emotion and reasoning. To explore if this is indeed the case, we analyze language in millions of books covering the period from 1850 to 2019 represented in Google nGram data. We show that the use of words associated with rationality, such as determine and conclusion, rose systematically after 1850, while words related to human experience such as feel and believe declined. This pattern reversed over the past decades, paralleled by a shift from a collectivistic to an individualistic focus as reflected, among other things, by the ratio of singular to plural pronouns such as I/we and he/they. Interpreting this synchronous sea change in book language remains challenging. However, as we show, the nature of this reversal occurs in fiction as well as nonfiction. Moreover, the pattern of change in the ratio between sentiment and rationality flag words since 1850 also occurs in New York Times articles, suggesting that it is not an artifact of the book corpora we analyzed. Finally, we show that word trends in books parallel trends in corresponding Google search terms, supporting the idea that changes in book language do in part reflect changes in interest. All in all, our results suggest that over the past decades, there has been a marked shift in public interest from the collective to the individual, and from rationality toward emotion.

Automated summary

The research suggests that there has been a gradual increase in the use of words associated with rationality in books since 1850, while words related to human experience have decreased. In recent decades, this pattern has reversed, accompanied by a shift from collectivism to individualism and changes in the ratio between sentiment and rationality flag words. Overall, there has been a marked shift in public interest from collective to individual, and from rationality towards emotion in recent decades.