The most common way to signify possession in English is by using an apostrophe.
That is Mika’s coat.
Is that Mr. Johnson’s car?
Though this is easy enough to understand, there are some common mistakes when using possessive apostrophes.
‘S and s’s
The one which people have the most trouble with is what to do when the noun ends in an “s.”
This confusion is understandable because people have different preferences about how to do this. The truth is that there are two acceptable ways to punctuate singular possessive nouns.
Correct: What do you think of Chris’ report?
Correct: What do you think of Chris’s report?
Both of these are acceptable, and they are spoken identically– something like, “Chris-iz”. On the other hand, plural nouns never get an additional “s” at the end, otherwise they would be incorrect or appear to revert back to the singular.
Correct
Stores’ inventory
Attorneys’ fee
Incorrect
Stores’s inventory
Attorneys’s fee
Recognize when you are distinguishing a singular subject and a plural subject. The following two examples are correct in representing the possession of a single store or attorney, but incorrect for showing possession for multiple stores or attorneys.
Correct for singular subject; incorrect for plural
Store’s inventory
Attorney’s fee
There are also a number of irregular plural nouns that are treated grammatically as singular subjects such as: media’s coverage or people’s beliefs.
Plural or possessive?
Another thing that gets people into trouble is when they confuse a noun that needs a possessive apostrophe for the plural form of the noun.
Incorrect: What is the companies policy regarding sick days?
Correct: What is the company’s policy regarding sick days?
The first sentence implies no possession at all. If I wanted to refer to the policy of multiple companies, I could write, “What is the companies’ policy…,” but the first sentence doesn’t make sense grammatically as is.
Misplacing the Apostrophe
You also want to be careful not to put the apostrophe in the wrong place. If someone’s last name ends with an “s,” you don’t want to put an apostrophe within their name.
Incorrect: Mrs. Rawling’s class
Correct: Mrs. Rawlings’ class or Mr. Rawlings’s class
Multiple Nouns and Compound Nouns
If you are referring to two or more subjects but the thing they are possessing is the same, you only add an apostrophe to the latter subject. For instance, “Kim and Roger’s house is very roomy.” If, however, you are referring to two people with two separate houses, “Andrew’s and Ralph’s houses are very roomy” is acceptable.
If you are using a compound noun, like mother-in-law or editor-in-chief, the apostrophe is used on the last word. So, mother-in-law’s and editor-in-chief’s.
Beyond the Apostrophe
There are, of course, other ways to indicate possession besides the apostrophe. The way to indicate possession in many other languages besides English (but also English) is to have the thing being possessed precede the possessor. Though, as discussed in the nominalization post, this inverts the typical and preferred syntactic structure, it is grammatically correct.
That is the company’s policy.
That is the policy of the company.
This construction should be used sparingly, not just because of the syntactic inversion, but because it can sound very unnatural. Most of the time, the apostrophe is the best way to indicate possession. It is not incorrect, but the sentence, “That is the coat of Mika” sounds strange to a native ear.
Possessive Adjective and Pronouns
Finally, the other way to indicate possession is by using possessive adjective like, my, your, his, her, its, their, our and possessive pronouns like, mine, yours, his, hers, its, theirs, and ours.
Possessive adjectives are used just like other adjectives in that they modify the noun to give more information.
Just as the adjective “nice” modifies the noun in the following sentence, we can exchange it for the word “my” to indicate possession.
That is a nice watch.
That is my watch.
Possessive pronouns, just like regular pronouns, take the place of the noun. And often it is taking the place of a noun modified by a possessive pronoun.
In response to the question, “Is that your watch?” You could respond with, “Yes, it’s my watch. If you don’t want to sound like a robot, however, it sounds more natural to say, “Yes, it’s mine,” where the pronoun mine replaces the established referent, my watch.
–Russell
Referenced Material:
http://www.grammarbook.com/punctuation/apostro.asp