An apostrophe is a mark of punctuation (') used to identify a noun in the possessive case or indicate the omission of one or more letters from a word. The apostrophe has two main jobs in English: to mark contractions and to indicate possession. While that may sound simple enough, many people are baffled by the little squiggle. The apostrophe is often misplaced or forgotten, and sometimes it shows up in words where it isn't needed at all. Although there will always be minor disagreements about usage, these six guidelines should help you decide when to use apostrophes, where to put them, and when to leave them out altogether.

How to Use Apostrophes to Make Contractions Use apostrophes to form contractions, where two or more words are combined to form one, with letters omitted. The apostrophe replaces the omitted letter(s). The classes of words that are most frequently affected by contractions are verbs and pronouns. For example, in the contractions I'm, let's, and you'll, the apostrophe replaced the a in I am, the u in let us and the wi in you will. The same goes for the word doesn't where the apostrophe replaces the o in not. A few examples of sentences that contain contractions include quotes from famous authors. The words containing contractions are in italics. The letters that make up the contraction, as well as the apostrophe that replaces missing letter(s), are indicated in boldface type.

"If you don't like something, change it. If you can't change it, change your attitude."

- Maya Angelou

"She wasn't doing a thing that I could see, except standing there leaning on the balcony railing, holding the universe together."

- J.D. Salinger

"Three o'clock is always too late or too early for anything you want to do."

- Jean Paul Sartre, "Nausea" Note that o'clock is a contraction for the full phrase of the clock, notes Merriam-Webster's Ask the Editor. Also, be careful to place the apostrophe where the letter(s) have been omitted, which is not always the same place where the two words have been joined.

How to Use Apostrophes With Single Nouns Use an apostrophe plus -s to show the possessive form of a singular noun, even if that singular noun already ends in -s. To form the possessive of singular nouns, add 's, as in Homer's job or the dog's breakfast. Some other examples include:

"The mother's heart is the child's schoolroom."

- Henry Ward Beecher

"I will not hide the teacher's medication."

- Bart Simpson, "The Simpsons​" Some style guides (including the "Associated Press Stylebook" but not "The Chicago Manual of Style") recommend using only an apostrophe after singular proper names ending in -s (for example, Achilles' heel and Tennessee Williams' plays). In general, ​follow your style manual or your own good sense, and be consistent.

How to Use Apostrophes With Plural Nouns To form the possessive of a plural noun that already ends in -s, simply add an apostrophe, as in the bankers' bonuses, the coaches' offices, and in these examples: The girls ' swing set (the swing set belonging to the girls)

swing set (the swing set belonging to the girls) The students ' projects (the projects belonging to the students)

projects (the projects belonging to the students) The Johnsons' house (the house belonging to the Johnsons) Note how some family names fall into this category, as in this example from Richard Lederer and John Shore's book, "Comma Sense."

"If you must announce possession, place the apostrophe after the plural names — the Smiths', The Gumps' and The Joneses'." To form the possessive of plural nouns that end in a letter other than s, add 's, as in the women's cars. Other examples include: The women 's conference (the conference belonging to the women)

conference (the conference belonging to the women) The children 's toys (the toys belonging to the children)

toys (the toys belonging to the children) the men's training camp (the training camp belonging to — or used by — the men)

How to Use an Apostrophe When Two or More Nouns Possess the Same Thing When two or more nouns possess the same thing, add an apostrophe plus -s to the last noun listed, as in: Ben and Jerry 's Cherry Garcia ice cream

Cherry Garcia ice cream Emma and Nicole's school project (Emma and Nicole worked together on the same project.) Note also how an example from section No. 3 — Richard Lederer and John Shore's book, "Comma Sense" — follows this rule. The book, "Common Sense" (or more specifically the authorship of the book), belongs equally to Lederer and Shore, so only the second name, Shore, takes the apostrophe and s. By contrast, when two or more nouns separately possess something, add an apostrophe to each noun listed: Tim 's and Marty 's ice cream (Each boy has his own ice cream.)

and Marty ice cream (Each boy has his own ice cream.) Emma's and Nicole's school projects (Each girl has her own project.)

Don't Use an Apostrophe With Possessive Pronouns Don't confuse the contraction it's (meaning it is) with the possessive pronoun its, as in: It's the first day of spring.

the first day of spring. Our bird has escaped from its cage. Because possessive pronouns already show ownership, it's not necessary to add an apostrophe: Yours

His

Hers

Its

Ours

Theirs However, you do add an apostrophe plus -s to form the possessive of some indefinite pronouns: Anybody 's guess

guess One 's personal responsibility

personal responsibility Somebody's wallet Note also how the contraction in the second sentence in this section does need the apostrophe: Because possessive pronouns already show ownership, it's not necessary to add an apostrophe (for a possessive pronoun, but it is necessary to use an apostrophe to form a contraction for it is, which becomes it'​s).