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Resource Summary: This page presents information about the apostrophe, as well as common apostrophe usage errors.
Last Updated: 05/17/11
Apostrophes are punctuation marks used to indicate possession. The placement of an apostrophe depends upon the word you are making possessive.
1. Singular possessive. Make a singular noun possessive by adding an apostrophe and an s.
Example: Long's theory (2003) suggested...
Note that singular nouns ending in s still take an apostrophe and an additional s (i.e., Jones's theory).
2. Plural possessive (regular). Make a plural noun possessive by adding an apostrophe.
Example: The Nurses' Association published a code of ethics...
3. Plural possessive (irregular). Make an irregular plural noun (such as women or children) possessive by adding an apostrophe.
Example: The Akron Children's Hospital..
Common Apostrophe Errors
There are some common apostrophe errors that are easy to avoid. Do not use an apostrophe:
1. When making a noun plural.
Incorrect: The studies' of Jones and Barnum...
Correct: The studies of Jones and Barnum... or Jones's and Barnum's studies...
2. When making an acronym or a number plural.
Incorrect: CEO's of major corporations in the 1950's...
Correct: CEOs of major corporations in the 1950s...
3. When constructing contractions. Though apostrophes can also be use to create contractions (words like can't and didn't), APA rules require writers to avoid contractions.
Incorrect: Walden University doesn't recognize Ground Hog Day as an official holiday.
Correct: Walden University does not recognize Ground Hog Day as an official holiday.