In their highly acclaimed craft book The Elements of Style, William Strunk Jr. and E.B. White say,
Form the possessive singular of nouns by adding ‘s.
Adding ‘s to a noun is often really easy and clear.
We do it in our writing every day without ever thinking about it.
I refer to examples like the following…
Sharon couldn’t stand Ben’s poems.
She really admired the film’s soundtrack.
The novel’s chapter lengths were highly intimidating.
You add ‘s to a noun to form a possessive singular, and boom, you’re done.
But what about nouns that end in the letter s?
This matter has given me confusion basically my entire life. One, because I’ve had teachers teach it both ways. And two, because the wrong way I always feel actually looks better in the sentence than the right way.
To this day, I might write a sentence like this:
He refused to get inside Thomas’ car.
Although the right way to write the sentence is like this:
He refused to get inside Thomas’s car.
Yes, even if the noun ends with the letter s, you should still add ‘s after.
I have a crush on Charles’s friend.
Beatrice stepped quietly inside Mr. Ness’s garage.
I think the ‘s looks especially awkward when a noun ends with two letters of s, like in that last example. But alas, that’s the right way, and so we need to stick to it!
What are some exceptions?
Like with most grammar rules, there are exceptions.
You don’t need ‘s for the possessives of ancient proper names ending in ‘es and ‘is and such forms as for conscience’ sake and for righteousness’ sake.
Keep in mind that pronominal possessives such as hers, its, theirs, yours, and ours don’t have an apostrophe.
And remember that it’s doesn’t means its! The first is a contraction meaning it is, while the second is a possessive.
Lastly, if the noun is plural, remember to add an apostrophe only, not an ‘s.
She really admired the three films’ soundtracks.
Barry couldn’t stand the dogs’ barking at the park.
The books’ odors made Mary surprisingly nostalgic.
Just keep in mind in almost every case to add ‘s for the possessive singular of nouns and to add only an apostrophe for the possessive plural of nouns.
Yes, even if it might look a little odd on the page!