The apostrophe has three uses:
1) to form possessives of nouns
2) to show the omission of letters
3) to indicate certain plurals of lowercase letters.
Apostrophes are NOT used for possessive pronouns or for noun plurals, including acronyms.
How to make a noun possessive: To see if you need to make a possessive, turn the phrase around and make it an "of the..." phrase. For example:
the boy's hat = the hat of the boy; three days' journey = journey of three days
Once you've determined whether you need to make a possessive, follow these rules to create one.
1. add 's to the singular form of the word (even if it ends in -s): the owner's car; James's hat
2. add 's to the plural forms that do not end in -s:
the children's game; the geese's honking
3. add ' to the end of plural nouns that end in -s:
houses' roofs; three friends' letters; the Joneses' car
4. add 's to the end of compound words:
my brother-in-law's money
5. add 's to the last noun to show joint possession of an object:
Todd and Anne's apartment
Showing omission of letters: Apostrophes are used in contractions. A contraction is a word (or set of numbers) in which one or more letters (or numbers) have been omitted. The apostrophe shows this omission. Contractions are common in speaking and in informal writing. To use an apostrophe to create a contraction, place an apostrophe where the omitted letter(s) would go. Here are some examples:
don't = do not
I'm = I am
he'll = he will
who's = who is
shouldn't = should not
didn't = did not
could've= could have (NOT "could of"!)
'60 = 1960
Forming plurals of lowercase letters: Apostrophes are used to form plurals of letters that appear in lowercase; here the rule appears to be more typographical than grammatical, e.g. "three ps" versus "three p's." To form the plural of a lowercase letter, place 's after the letter. There is no need for apostrophes indicating a plural on capitalized letters, numbers, and symbols (though keep in mind that some editors, teachers, and professors still prefer them). Here are some examples:
p's and q's = a phrase indicating politeness, from "mind your pints and quarts"
Nita's mother constantly stressed minding one's p's and q's.
three Macintosh G4s = three of the Macintosh model G4
There are two G4s currently used in the writing classrom.
many &s = many ampersands
That printed page has too many &s on it.
the 1960s = the years in decade from 1960 to 1969
The 1960s were a time of great social unrest.
Don't use apostrophes for possessive pronouns or for noun plurals. Apostrophes should not be used with possessive pronouns because possessive pronouns already show possession -- they don't need an apostrophe. His, her, its, my, yours, ours are all possessive pronouns.
I wrote an Apostrophe 101 document for training purposes. The areas of contention are:
Never, Never, Never, Ever use an apostrophe in a plural. Ever*.
In Britain this is known as "The Grocer's Apostrophe", presumably because they used to leave school at twelve to work in Dad's grocery shop. "Cabbage's 30p/lb", "Carrot's 50p/lb". Certain words, for instance those that end in 'x',can take "es" as an indication of plural or can retain the Latin form, e.g. "vertex" and "vertices". "Vertexes" is fine though. Certain collective nouns for animal remain the same as the singular, deer, sheep and moose, for instance. Others modulate, like "tooth/teeth" and "mouse/mice".
*In the matter of acronyms, although apostrophe-s is incorrect, it improves readability and is therefore becoming accepted. e.g. FRC's "Fellows of the Royal College" which means something different from FRCS "Fellow of the Royal College of Surgeons" . Pedant that I am, I can let that go by.
Apostrophe - s, unless the word ends in s, in which case just tack an apostrophe on the end. e.g. "Keeping up with the Jones'" and not "the Jones's" or "Joneses. "Bill's dogs' vet bills were mounting"Contractions:
An apostrophe can indicate missing letters, e.g. "should've" and "could've" for "should have" and "could have". And NOT "should of" or "could of".
"He wait's for a bus". "Mom go's to the mall". Should be "He waits for a bus" and "Mom goes to the mall". When stating the verb forms for those categories of the person that end in 's' you MUST NOT use an apostrophe.
you dont use an apostrophe in will not
you do not use an apostrophe in cultures.
You can't use congratulations with an apostrophe.
You use an apostrophe when someone owns something such as "Ben's Car". You also use an apostrophe to shorten something such as "That is beautiful" when you shorten it with an apostrophe it would be " That's beautiful". HOPE I HELPED
One should never use an apostrophe for the word that.One should always use an apostrophe for the word that's, meaning that is.
Use apostrophe S for singular nouns that have possession - example "cat's tail." Use a single apostrophe at the end of a plural noun that ends in S - example "Use the boys' room."
Same as any other use. Use an apostrophe S to indicate possession.
An apostrophe is used in contraction. Example: you will: you'll
It's This '
it's (as in it is)