Good authors, too, who once knew better words now only use four letter words writing prose…anything goes!
Actually, I wonder if this tells us less about when words or phrases were used, and more about how many books are digitally catalogued from those time periods.
Oh, there’s obviously a social mores aspect to the whole books ngram results, and I agree there has to be some function of the number of books from each time period as well as OCR ability over time. (Not sure if they continuously update the OCR results as tech gets better or if they just let the early scans sit as is.)
On a common theme… I was searching the newly released 1950 us census for family at lunch.
The National Archives used software to turn the handwriting into searchable text. Did a fairly good job, but still lots of weirdness. Looks like the software got a little flustered in the middle, there.