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Just as all punctuations marks ensure the clarity of writing for readers, apostrophes function to clarify the function of nouns by indicating possession and showing omissions. Apostrophes perform three basic functions.
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1. Use apostrophes to form possessive nouns. Add an apostrophe and an s with the apostrophe before the s for singular nouns including compound nouns that end in any letter except s. For example:
- puppy's ball
- Mark's truck
- father-in-law's farm
- queen of England's castle
Add an apostrophe after the final s for singular nouns that end in s. For example:
- platypus' eggs
- walrus' tusks
- James' family
- Jesus' apostles
Add an apostrophe after the s plural marker for plural nouns that end in s. For example:
- brothers' girlfriends
- students' essays
- walruses' tusks
- kittens' yarn
Add an apostrophe and an s with the apostrophe before the s for plural nouns that end in any letter except s. For example:
- alumni's gift
- mice's cage
- geese's nests
- children's toys
Follow the above rules for singular and plural nouns and place the possessive marker after the final noun for joint possession. For example:
- mom and dad's house
- sister, brother, and cousin's toys
- dogs and cats' pen
- students, parents, and teachers' handbooks
Follow the above rules for singular and plural nouns and place the possessive markers after each noun for individual possession. For example:
- mom's and dad's houses
- sister's, brother's, and cousin's toys
- dogs' and cats' pens
- students', parents', and teachers' handbooks
- *You need to clean your's. (incorrect)
- You need to clean yours. (correct)
- *His' book is on the table. (incorrect)
- His book is on the table. (correct)
Do not use apostrophes with compound nouns. For example:
- *hotel's room (incorrect)
- hotel room (correct)
- *table's leg (incorrect)
- table leg (correct)
Do not use apostrophes with plural nouns. For example:
- *The dogs' played in the park. (incorrect)
- The dogs played in the park. (correct)
- *We left our cars' in the parking lot. (incorrect)
- We left our cars in the parking lot.
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Contractions and omissions
2. Use apostrophes to form contractions. Contractions are words in which two words combine into a single word through the omission or combination of sounds and letters. The use of contractions in written and spoken English is acceptable in all but the most formal writing settings. For example:
- aren't (are not)
- can't (cannot)
- don't (do not)
- he's (he is)
- I'm (I am)
- isn't (is not)
- it's (it is)*
- mustn't (must not)
- she'd (she had/she would)
- that'd (that would)
- there's (there is)
- they've (they have)
- 'twas (it was)
- we're (we are)
- won't (will not)
- you're (you are)
*Note that its without an apostrophe is the third person singular neuter possessive pronoun and that it's with an apostrophe is the contraction of it is.
Also use apostrophes to indicate other omissions of letters and sounds. For example:
- I was born in '85. (1985)
- The '60s were a time of great social change. (1960s)
- The raven cried, "Ne'ermore!" (Nevermore)
- Are you talkin' to me? (talking)
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Pluralize lowercase letters and words used as words
3. Use apostrophes to pluralize lowercase letters. Also use apostrophes to pluralize words used as words. For example:
- You ought to mind your p's and q's.
- Please color all the a's red and all the b's blue.
- You misspelled all the their's in your paper.
- Good writers avoid using excessive it's in their writing.
Do not use apostrophes to pluralize capital letters, numbers, symbols, and acronyms. For example:
- The Ps are located on the sixth floor of the library.
- Only the richest and most famous can afford to own G5s.
- Please replace the &s in your essays with and's.
- All applicants must have PhDs.
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The accompanying printable reference sheet of the rules for using colons in English is available for download at The Use of Apostrophes in Written English Reference Sheet.