Brendan Duong points me to another Google innovation, a new way of tracking mentions of words and terms in books, using the huge archive of scanned books in Google Books. It can be used to track ideological fashion and interest over time.
In the easy to use version (there is a complicated-looking raw data download option) some care has to be taken with interpreting the results. For single words it is calculated as a % of all ‘unigrams’ or single words, for two-word phrases it is a % of all ‘bigrams’ or two-words. So percentages will always be lower for bigrams than unigrams, and I won’t directly compare them.
And because we are looking at percentages of all words in the category, a term could be rising in absolute mentions but still declining relatively.
Over the 150 years to 2000, we can see the changing fortunes of the three main Western ideological forces: socialism, liberalism, and conservatism. The interest of intellectuals in socialism is very evident here. Despite socialism entering a long decline in the 1980s, in 2008 it was still more mentioned slightly more often than liberalism. And despite the apparent ideological revival of conservatism, it trended slightly down from the 1960s.
[19/12: graphs and text updated to take account of later data]