At Knowledge Keepers, we love primary source documents, and encourage every American to read them as often as possible. That’s why we reprint the good old books in our Home Library Series. When reading old manuscripts and documents, we run into a common question: Why do they sometimes use an “f” in the place of an “s”?

This is called a long or leading s, a character that looks similar to the letter “f” but is used as an “s,” often as the first of a “double s” as in assign or address.

Take the Virginia Constitution of May 6, 1776:

Though it looks like an “f” to us, it really is another form of “s.”

Look closely.

“In Eighteenth century writing two different forms of the letter “s” appear in both printed and handwritten works. The regular “s” which is still used today, and the “long S.”

“It’s sometimes hard to see the difference between the long S and the letter F. The horizontal bar goes all the way through the vertical stem of the letter ‘f’ but only extends to the left of the vertical stem of the long S in printed works.” (Source)

There’s a lot more info on the history of this part of the English language in the detailed post at Babel Stone Blog, where I found this list of “Long S rules:

Rules for Long S in English

The following rules for the use of long s and short s are applicable to books in English, Welsh and other languages published in England, Wales, Scotland, Ireland and other English-speaking countries during the 17th and 18th centuries.

• short s is used at the end of a word (e.g. his, complains, ſucceſs)
• short s is used before an apostrophe (e.g. clos’d, us’d)
• short s is used before the letter ‘f’ (e.g. ſatisfaction, misfortune, transfuſe, transfix, transfer, ſucceſsful)
• short s is used after the letter ‘f’ (e.g. offset), although not if the word is hyphenated (e.g. off-ſet) [see Short S before and after F for details]
• short s is used before the letter ‘b’ in books published during the 17th century and the first half of the 18th century (e.g. husband, Shaftsbury), but long s is used in books published during the second half of the 18th century (e.g. huſband, Shaftſbury) [see Short S before B and K for details]
• short s is used before the letter ‘k’ in books published during the 17th century and the first half of the 18th century (e.g. skin, ask, risk, masked), but long s is used in books published during the second half of the 18th century (e.g. ſkin, aſk, riſk, maſked) [see Short S before B and K for details]
• Compound words with the first element ending in double s and the second element beginning with s are normally and correctly written with a dividing hyphen (e.g. Croſs-ſtitch, Croſs-ſtaff), but very occasionally may be written as a single word, in which case the middle letter ‘s’ is written short (e.g. Croſsſtitch, croſsſtaff).
• long s is used initially and medially except for the exceptions noted above (e.g. ſong, uſe, preſs, ſubſtitute)
• long s is used before a hyphen at a line break (e.g. neceſ-ſary, pleaſ-ed), even when it would normally be a short s (e.g. Shaftſ-bury and huſ-band in a book where Shaftsbury and husband are normal), although exceptions do occur (e.g. Mans-field)
• double s is normally written as double long s medially and as long s followed by short s finally (e.g. poſſeſs, poſſeſſion), although in some late 18th and early 19th century books a different rule is applied, reflecting contemporary usage in handwriting, in which long s is used exclusively before short s medially and finally [see Rules for Long S in some late 18th and early 19th century books for details]
• short s is used before a hyphen in compound words with the first element ending in the letter ‘s’ (e.g. croſs-piece, croſs-examination, Preſs-work, bird’s-neſt)
• long s is maintained in abbreviations such as ſ. for ſubſtantive, and Geneſ. for Geneſis (this rule means that it is practically impossible to implement fully correct automatic contextual substitution of long s at the font level)

So when did Americans finally switch to the exclusive form of S? The History of Information site says, “Long ‘s’ fell out of use in Roman and italic typography well before the middle of the 19th century; in French the change occurred from about 1780 onwards, in English in the decades before and after 1800, and in the United States around 1820. This may have been spurred by the fact that long ‘s’ looks somewhat like ‘f’ (in both its Roman and italic forms), whereas short ‘s’ did not have the disadvantage of looking like another letter, making it easier to read correctly, especially for people with vision problems.”