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Apostrophe errors often occur when the plural form and the possessive form are confused. Additionally, apostrophes also tend to be used incorrectly with years.

Incorrect: Joneses yard is much bigger than Smith's.
Incorrect: My brother graduated from NIU in the early 1990's.

Correcting the Problem

Correct: Jones's yard is much bigger than Smith's.
Correct: My brother graduated from NIU in the early 1990s.

Rule to Remember

The apostrophe is used to indicate posessive case, contractions, and omitted letters.

The apostrophe is not strictly a punctuation mark, but more a part of a word to indicate possessive case, contractions, or omitted letters.


Apostrophes are used to form the possessive form of a singular noun or a plural noun not ending in s by adding ' and an s at the end. If a plural noun ends in s, only ' should be added.

university's women's students'

Correct: High school students' scores have been gradually improving over the last several years.

If ownership of something is shared, use 's after the second owner.

Correct: Bill and Ted's guitar

If ownership of something is separate, use 's after each owner.

Correct: Bill's and Ted's guitars

Rule to Remember

If ownership of something is shared, use 's after the second owner; otherwise, use 's after each owner.


A contraction is one word that is formed by combing two words. As the two words are combined, a letter is (letters are) dropped and an apostrophe is added in its place. Usually, a pronoun and a verb are used when forming contractions.

The following is a list of common contractions:

'd when contracting would or had (he'd)
'm when contracting am (I'm)
's when contracting is or has (she's)
'll when contracting will (I'll)
're when contracting are (they're)
've when contracting have (we've)
n't when negating some helping or linking verbs (wasn't, shouldn't)

Correct: They'll complete the assignment by tomorrow.

Not is used to form negative contractions with many linking verbs. When making a negative contraction, omit the "o" in "not" and replace it with an apostrophe. The only exception to this rule is will not which contracts to form won't.

Correct: Don't take my car!

Numbers and Omissions

Numbers can be shortened by adding an apostrophe in place of the omitted number.

Correct: the class of '07
Correct: events in the '60s

Be careful using abbreviations in formal writing. In most cases, it is best to spell the numbers out or write them as full numerals.

Rule to Remember

Numbers can be shortened by adding an apostrophe in place of the omitted number.

Plurals of Letters, Words, Numbers, and Signs

An apostrophe and s are also used to form the plural of letters, numbers, signs, and words referring to words.

Correct: The word Mississippi has many s's.
Correct: Count incorrectly spelled accent's in your essay.

When Do You NOT Need an Apostrophe?

With time periods and after numbers

Incorrect: The 1900's = the years between 1900-1999
Correct: The 1900s = the years between 1900-1999
Incorrect: MP3's = more than one MP3
Correct: MP3s = more than one MP3

Rule to Remember

Do not add an apostrophe at the end of a number indicating a time period: 1960s, 1800s, etc.

After symbols:

Correct: *s = asterisks
Correct: #s = pounds/numbers

After abbreviations:

Correct: CDs = compact disks
Correct: DVDs = digital video (or versatile) disks

With possessive pronouns:

its, hers, his, theirs, my, mine, ours, yours, whose

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