Society and culture:
From a current day academic point of view society and culture are separate but related concepts. Culture tends to refer to the values and beliefs of a group of people and the material surroundings that evidence those values and beliefs. Society tends to refer to the group itself, defined by the cultural infrastructure. But there’s a lot of overlap in academic use. And popular use is even more complicated.
Society when I was growing up had a values connotation: why do I have to do what society says? This is the use of the word in Janis Ian’s Society’s Child. Why should “society” tell me not to love who I want to love?
Then there was also the use of the word as shorthand for “high society”. This was the use of the word in Cleveland Amory’s Who Killed Society? That book came out in 1960 but was about the decline of Gilded Age fortunes earlier in the century.
As the Ngram indicates society has a longer history of common use than culture. Culture has always had it own “high” side, with high culture (Beethoven) contrasted with pop culture (Beatles). But we see a steady ascent in the early 20th century, and this may be due to the rise of popular anthropological ideas from people like Margaret Mead and Franz Boas. There’s also a morphing that has taken place with the mash-up between high culture and low culture (see: Warhol) with the net result being a rise in the use of the word culture as an all-purpose descriptor of things related to the arts, literature, music (as in “culture blog”). So you can see a rise in term culture and that it begins to put pressure on the term society.
Then, with culture still steadily on the rise, society sees a big spike in the sixties through the mid-seventies. I expect this was the high point of the Janis Ian, counterculturally-inflected use of the term as one of disparagment. Then society heads into a tailspin as culture makes a large leap, continuing to the present day.
Ngram is of course able to track usage and can’t track shifts in meaning quite as well. Perhaps you have to use proxies like debutante versus income inequality.
Mickey Kaus writes that we focus too much on income inequality and not enough on a growing but still not-remarked-upon social inequality. The return of “society” perhaps, in the Amory sense of the term? Maybe the lines will shift again.