Q: I am curious why some of us were taught to use an apostrophe plus “s” to make a possessive of a singular proper noun ending in “s,” “x,” or “z,” while others were taught to use just an apostrophe.
A: Many people don’t realize that the conventions of punctuation are largely matters of style, and they’re much more fluid than the conventions of grammar. As we noted in a 2011 post, the customs of punctuation sometimes shift.
We wrote that an apostrophe plus the letter “s” has generally been used to mark the possessive case of singular nouns for at least three centuries, and that this has been true whether or not the nouns ended in a sibilant like “s,” “x,” or “z.”
Fowler’s Dictionary of Modern English Usage (4th ed., edited by Jeremy Butterfield) has this to say:
“The apostrophe before s became regulated as an indication of the singular possessive case towards the end of the 17c., and the apostrophe after s was first recorded as an indication of the plural possessive case towards the end of the 18c.”
Fowler’s says these “basic patterns” apply to proper names ending in “s.” So add an apostrophe plus “s” to a singular name, Butterfield writes, “whenever you would tend to pronounce the possessive form of the name with an extra iz sound, e.g. Charles’s brother, St James’s Square, Thomas’s niece, Zacharias’s car.”
However, he notes that “gross disturbances of these basic patterns have occurred in written and printed work” since then, and “further disturbances may be expected in the 21c.”
In the mid-20th century, it was not uncommon to be taught to drop the possessive “s” and use only an apostrophe after words ending in a sibilant (as in “Charles’ brother”). Although this isn’t a common practice today, it’s still sometimes seen in published writing.
The Chicago Manual of Style (17th ed.) says some writers and publishers still prefer a system “of simply omitting the possessive s on all words ending in s.” However, the manual says that this system is “not recommended” because it “disregards pronunciation.”
This is what the Chicago Manual advocates: “The possessive of most singular nouns is formed by adding an apostrophe and an s. … The general rule stated at [that paragraph] extends to the possessives of proper nouns, including names ending in s, x, or z.”
The examples given in the Chicago Manual include “Kansas’s legislature,” “Marx’s theories,” “Berlioz’s works,” “Borges’s library,” and “Dickens’s novels.”
To show just how changeable these customs can be, we wrote a post in 2018 on shifts in possessive forms of ancient classical or biblical names that already end in “s,” like “Moses” and “Euripedes.”
The traditional custom had been to add just an apostrophe, but in current practice the additional “s” is optional, depending on whether or not it’s pronounced: “Euripides’ plays” or “Euripides’s plays,” “Moses’ staff” or “Moses’s staff,” “Jesus’ teachings” or “Jesus’s teachings.”
As Pat writes in the new fourth edition of Woe Is I, “Let your pronunciation choose for you. If you add an extra syllable when pronouncing one of these possessive names (MO‑zus‑uz), then add the final s (Moses’s). If you don’t pronounce that s (and many people don’t, especially if the name ends in an EEZ sound, like Euripides), then don’t write it.”