Possessive of Proper Names Ending in S

The questions on the use of the apostrophe to form the possessive keep coming. This post is about how to form the possessive of a proper name that ends in -s. 

Most stylebooks agree that the rule for forming the possessive of a singular noun ending in -s is formed by adding ’s:

the boss’s birthday
the bus’s wheels
the witness’s testimony

When it comes to forming the possessive of a proper name that ends in s, guides disagree. 

Some stylebooks recommend a single apostrophe for Biblical or classical names like Jesus and Achilles, but ’s for names like James and Charles; others say, “Treat all names ending in s the same.”
The Chicago Manual of Style once recommended a single apostrophe to form the possessive of Biblical or classical names:

Moses’ tent
Achilles’ helmet
Jesus’ name

Some guides still recommend this usage, but CMOS has changed its policy in a spirit of consistency; now it recommends that all proper names ending in -s form their possessive by adding ’s:

Moses’s tent
Achilles’s helmet
Jesus’s name
Travis’s friends
Dickens’s novels
Descartes’s philosophy
François’s efforts
Tacitus’s Histories
Kansas’s legislature
Euripides’s tragedies
the Ganges’s source

Equally consistent, the Associated Press Style Book opts for a single apostrophe for all proper names ending in -s:

Moses’ tent
Achilles’ helmet
Jesus’ name
Travis’ friends
Dickens’ novels
Descartes’ philosophy
François’ efforts
Tacitus’ Histories
Kansas’ legislature
Euripides’ tragedies
the Ganges’ source

The New York Times style manual generally agrees with CMOS, but adds this wrinkle:

Omit the s after the apostrophe when a word ends in two sibilant sounds…separated only by a vowel sound: Kansas’ Governor; Texas’ population; Moses’ behalf… But when a name ends with a sibilant letter that is silent, keep the possessive s: Arkansas’s…

Disagreement on the issue of apostrophe s vs. plain apostrophe goes all the way to the Supreme Court. Justice Clarence Thomas believes that the possessive form of a name like his should be formed by adding only an apostrophe: “Justice Thomas’ opinion.” Referring to the case Kansas v. Marsh (2006), Thomas wrote “Kansas’ statute,” but his colleague Justice Souter wrote “Kansas’s statute.”

If you write for publication, how you treat the possessive of proper names that end in -s will be determined by your employer’s house style.
If you are free to choose which style to follow, keep in mind that the writer’s goal is to convey thoughts as clearly as possible to readers. Style guides exist to assist writers in this goal, but it seems to me that there are problems with the recommendations of all three guides mentioned above.
I prefer the guidelines given in the Penguin Guide to Punctuation:

A name ending in s takes only an apostrophe if the possessive form is not pronounced with an extra s. Hence: Socrates’ philosophy, Ulysses’ companions, Saint Saens’ music, Aristophanes’ plays.

The reasoning behind this rule is that as we don’t say [sok-ru-teez-iz], there’s no reason to write “Socrates’s.” 

Punctuation is supposed to aid readers, not puzzle them. It’s no help to readers unfamiliar with English pronunciation to mislead them into trying to say [dick-inz-iz], or [u-rip-uh-deez-iz] by writing “Dickens’s novels” or “Euripides’s plays.” 

The bottom line is that stylebooks do not agree on whether to write “Jesus’ name” or “Jesus’s name,” “Travis’ friend” or “Travis’s friend.” Writers not bound by a specific style manual must make their own decision and be consistent with it. Personally, I’d write “Jesus’ name” and “Travis’s friend” because I would say “[jee-zus] name” and “[trav-is-iz] friend.”

Source: Daily Writing Tips

So there you have it...they agree to disagree. Oh well!