I used to make a living as a programmer. I’m a numbers guy—I believe what data tells me. Now that I write fiction, I see writers comment on such things as how many semicolons to use or how long sentences should be. It is thus I came to write computer programs to analyze books, focusing on bestsellers.
The fit is probably not a straight line, otherwise we would expect to see sentences of only one word by the end of the 23rd century. Maybe.
Some of the decline in sentence length is attributable to the alarming die-off of semicolons, which may have been domesticated in earlier times to take on the burden of joining sentences.
Not quite gone yet, but by mid 2017 they will be extinct unless action is taken to protect these fragile creatures. Perhaps semicolon sanctuaries could be funded by a consumption tax on periods, question marks (below), and em-dashes, all of which are on the rise amongst punctuation consumers.
Is it ? use or ? abuse?
Although uncommon in everyday use, they enjoy increasing popularity in fiction.
Punctuation in the balance:
Despite the imminent extinction of semicolons, colons are merely endangered.
Exclamation points are in decline as well, although their number has been relatively stable since about 1960 despite many literary pundits advocating the extermination of these frightening creatures.
Commas, the farm animals of punctuation, have declined somewhat, but they still roam every book in the thousands.
The good news is that the abundance and diversity of punctuation overall has actually increased. There is little fear that our grandchildren will only encounter ellipses in zoos.