Have you ever looked at a picture of a really old document or an inscription on the wall of an old building and thought, “Why are there F’s instead of S’s? Did F stand for S back then?” But no, it’s only some of the S’s that look like F’s, not all of them: You’ll see both letters right next to each other, so it’s not like they didn’t have the letter S back then. Confusing, right?
The answer lies in the fact that that’s not an F at all. It’s actually a letter called the medial S, also known as the long S, which was a second form of the lowercase letter S. This old-fashioned letter has a long history. It’s derived from the Roman cursive S, and it survived as the Old English S, then onward through the history of English orthography until the 1800s.
The history of S is a twisting, turning path. Until around the 1100s or so, the medial S was the lowercase form of the letter, while the curvy line we use today was the uppercase form. But over time, the regular S, technically known as the “round S” or “short S,” started being used as a lowercase letter, too. By the 1400s, a new set of S usage rules was established: The medial S would be used at the beginning of a lowercase word or in the middle of a word, while the round S would appear either at the end of a word or after a medial S within a word, as in “Congreſs” (which appears in the first line of Article I of the Constitution).
Why did the old S go away? The answer lies largely in the use of the printing press. After all, why should printers keep two different forms of the lowercase letter S around when they could just use one and the words would still be readable? And if you have to choose one symbol for S, it only makes sense to choose the one that isn’t easy to mistake for an F.
Today, few people use this old-fashioned letter, but the Old English S did survive as a piece of mathematical notation. In calculus, the integral symbol ∫ is derived from the first letter of the word “summa,” Latin for “sum,” back when it would have started with a medial S. You’ll also see the early S behind the bar of many drinking establishments: It’s in the logo on every bottle of Jägermeister (or should that be “Jägermeiſter”?).