During the 1700's this country had no public schools and the general public was probably better educated than today's general public. Thomas Paine's Common Sense is difficult reading, yet it "sold over one hundred fifty thousand copies in its first printing (not counting England and Ireland). Eventually over five hundred thousand copies were sold."
"there were estimated to be only 2.5 million people living in the original thirteen colonies in 1776." That means one of every five people bought Common Sense, and undoubtedly more people than that read it.
Today's average high school graduate probably lacks the ability to read it. Here are the first three paragraphs:
PERHAPS the sentiments contained in the following pages are not yet sufficiently fashionable to procure them general favor. A long habit of not thinking a thing wrong gives it a superficial appearance of being right, and raises at first a formidable outcry in defense of custom. But the tumult soon subsides. Time makes more converts than reason.As a long and violent abuse of power is generally the Means of calling the right of it in question (and in Matters too which might never have been thought of, had not the Sufferers been aggravated into the inquiry), and as the King of England hath undertaken in his own Right to support the Parliament in what he calls Theirs, and as the good people of this country are grievously oppressed by the combination, they have an undoubted privilege to inquire into the pretensions of both, and equally to reject the usurpation of either.
In the following sheets, the author hath studiously avoided everything which is personal among ourselves. Compliments as well as censure to individuals make no part thereof. The wise and the worthy need not the triumph of a pamphlet; and those whose sentiments are injudicious or unfriendly will cease of themselves unless too much pains are bestowed upon their conversion.
3,000 is considered the minimum needed to communicate at basic level.
5,000 words, to put it in perspective, is about a third grade reading level.
To read Shakespeare easily you need a vocabulary of 20,000 words. To read him fluently you need a vocabulary of 30,000 words.