How did the content of books, or rather the words used in books, changed during the past 50 years? This is the research question tackled by Acerbi et al. from the university of Bristol in a new research paper. The researchers looked at how frequently ‘mood’ words were used through time in a database of more than five million digitised books provided by Google. The list of words was divided into six categories (anger, disgust, fear, joy, sadness, surprise).

From the press release:

In applying this technique, the researchers made some remarkable discoveries about the evolution of word usage in English books over the past century. Firstly, the emotional content of published English has been steadily decreasing over the past century, with the exception of words associated with fear, an emotion which has resurged over the past decades.

They also found that American English and British English have undergone a distinct stylistic divergence since the 1960s. American English has become decidedly more ’emotional’ than British English in the last half-century.

The same divergence was also found in the use of content-free words, that is words which carry little or no meaning on their own, such as conjunctions (‘and’, ‘but’) and articles (‘the’).

While the trends found in this study are very clear, their interpretation is still open. A remaining question, the authors say, is whether word usage represents real behaviour in a population, or possibly an absence of that behaviour which is increasingly played out via literary fiction. Books may not reflect the real population any more than catwalk models reflect the average body.

Abstract of the research published freely in PlosOne:

We report here trends in the usage of “mood” words, that is, words carrying emotional content, in 20th century English language books, using the data set provided by Google that includes word frequencies in roughly 4% of all books published up to the year 2008. We find evidence for distinct historical periods of positive and negative moods, underlain by a general decrease in the use of emotion-related words through time. Finally, we show that, in books, American English has become decidedly more “emotional” than British English in the last half-century, as a part of a more general increase of the stylistic divergence between the two variants of English language.