Lois’ blanket. Thomas’ Book. Jesus’ followers.
Does the apostrophe at the end of the above names take the place of the letters ES? I pronounce the missing ES at the end of the names: Loises blanket, Thomases book, Jesuses followers; and would do the same with any other names that end with S. My father-in-law says I’m incorrect. He says the ES should not be used: Lois blanket, Thomas book, Jesus followers. Please settle our dinner time debate, Thanks!
Your way is the only way I have ever heard others say it.
To start off with, this is not the traditional way to form such possessives. The Chicago Manual of Style and most other style guides recommend forming most possessives, even those ending with “s”, with an apostophe + s:
Lois’s blanket. Thomas’s book. Jesus’s followers.
However, practice varies. Many style guides allow dropping the “s” in the case of names with many syllables, and in the case of some Biblical names like Moses and Jesus. Some writers do so in all cases.
In my experience, following the traditional spelling, in most such possessives the “s” is pronounced: Loises, Thomases, Jesuses.
From Wiki
I’ve heard of the exception for Biblical and classical figures, but I find that it really is only used in stock phrases such as “Jesus’ sake” and “In Jesus’ name we pray, amen.”
(This is almost completely irrelevant, but an interesting and analogical highlight: I found out that in German, they apparently use the Latin genitive with certain religious names instead of the German one, at least in certain fixed phrases, such as Christi Geburt (the birth of Christ) rather than Christs Geburt or Mariä (for the Latin Mariæ) Himmelfahrt (the assumption of Mary). The normal genitive would be used for other women named Maria.)
I’ve certainly never come across any authoritative source suggesting that pronouncing the possessive with an ordinary schmo’s name (Charles’s dog, Burns’s suit) is incorrect.
This is the way I was taught, since the second “s” is pronounced as an additional letter.
written: both forms are correct
spoken: the “es” sound added is the norm.
If you don’t say the “es” it is not going to be apparent that it is a possessive. Clarity, as well as custom, demands that you pronounce it.
(Anyway, isn’t it a law of nature that fathers-in-law are always wrong?) 
Just popping in to say that you misused “it’s” in your title.
My experience is that the s followed by an apostrophe is pronounced longer, and is not voiced before a vowel or voiced consonant, unlike one preceded by an apostrophe.
himmelfahrt???!! goodness german is a funny language. i’m gonna suggest this to a friend who is trying to stop using profanity.
does that translate out to heaven-fast?
I agree that it should be written Thomas’s and pronounced as such.
I think “Heaven-driven”. Think Fahrvergnügen.
No – “Fahrt” means “journey” in German. “Himmelfahrt” literally means “journey to Heaven”.
I agree with the majority, but still think that it looks funny to write: Bess’s blanket, and it sounds funny to pronounce: Jesus’s beard.
-Greg
Every time I try to translate something based on my very meager knowledge of a foreign language vocabulary, I have greater sympathy for some of our clients’…interesting…grasp of English…
While we are at it:
it’s = it is, it has
its = that which belongs to it
in its possessive form
The rule I read recently - yes, you add the " 's" and pronounce the extra “S” as if it were an additional “es”, if that’s the way the plural is pronounced.
Lois’s pronounced “Loises”. “There were five Loises in a row on the catwalk.”
The exception, I read, is worded that already end with an “es” sound - the prominent one being “Jesus”. It’s grammatically best to say “Jesus’ book” as “Jee-zuz boo-k”. The possessive is understood - we hope. Can’t think of a similar “uz” word that would otherwise be wrongly pronuonced “…zuz-zuz”.
Moses.
I say “Jee-zuss” with an “s,” not a “z” sound at the end. As for similar words, “Prius” (e.g. the “Prius’s bumper.”) If you want the voiced sibilant, how about “missus”? As in “that’s the missus’s car.” I definitely pronounce the possessive “s” in all cases. It sounds weird to me not to.
the way that i learned it in both MD and VA public schools(not that it’s the ultimate authority or anything) was that you tack on the 's for proper nouns e.g. keeping up with the Jones’s.
however if the word isn’t a proper noun and ends in ‘s’ then you do the s’. i did enough rote busywork to know this for a fact and do not need a cite.