Use an apostrophe mainly to show possession or missing letters in a contraction; in a narrower convention, it can form the plural of a lowercase letter. Do not add one just to make an ordinary noun plural. Purdue OWL summarizes these uses and notes that possessive forms vary by style in some cases. [1]
Possession: ask who or what owns it
For a singular noun, a common pattern is to add apostrophe plus s: “the poet’s notebook,” “the bus’s route.” For a plural noun already ending in s, add the apostrophe after the s: “the poets’ notebooks.” For an irregular plural that does not end in s, add apostrophe plus s: “the children’s chorus.” Purdue gives these patterns and advises checking the relevant style guide when a singular name ends in s. [1]
A useful check is to rephrase the relationship with of: “the notebook of the poet” becomes “the poet’s notebook.” The test helps identify possession, but not every phrase with of needs an apostrophe. “The door of the studio” can simply be “the studio door.”
Contractions: show what is missing
In contractions, the apostrophe marks omitted letters: “we’re” for “we are,” “can’t” for “cannot,” and “they’ve” for “they have.” Put it where the missing letters belong. This is why “could’ve” represents “could have”; writing “could of” mistakes the sound of the contraction for its spelling. [1]
Contractions often suit speech and informal prose, though the best choice depends on context and voice. In a spoken-word draft, “I’m here” may sound closer to a speaker’s natural rhythm than “I am here.” In a formal notice, a writer may choose the expanded form for a more deliberate tone.
Three common lookalikes
“It’s” means “it is” or “it has”; “its” is possessive: “It’s lost its cover.” Expand the contraction to check it: “It is lost its cover” does not work, so the first form is “It’s,” and the second remains “its.” Possessive pronouns such as yours, hers, and ours also do not take apostrophes. [1]
“Who’s” means “who is” or “who has”; “whose” asks who something belongs to: “Who’s carrying the poster?” and “Whose poster is this?” The same expansion test works for who’s. For “whose,” ask about ownership instead.
An ordinary plural does not need an apostrophe: “three folders,” “two rehearsals,” “the 1990s.” Purdue notes a limited case for lowercase letters, as in “mind your p’s and q’s,” where the mark makes the letter easier to read. Styles can differ about apostrophes with abbreviations, numbers, and names ending in s, so follow a publication’s house style for those cases. [1]
A quick sorting exercise
Imagine a notice for an invented neighborhood reading: “The writers' table is near the door. Its sign says the event's open to visitors. Two reader's will introduce their poems.” Review every apostrophe by asking what job it performs. If the table belongs to multiple writers, “writers’ table” is right. If the sign belongs to the event, “event’s” shows possession, but “it’s” should appear only if the intended words are “it is.”
The final phrase means more than one reader, not something owned by one reader, so write “Two readers will introduce their poems.” If the sentence meant the poems belonged to two readers, write “Two readers’ poems will be introduced.” Reading the words aloud will not always resolve these differences; expand contractions and check who owns what.
Proofread the marks you added
A reliable edit starts by checking every apostrophe individually. Can you explain it as a possessive, a contraction, or a lowercase-letter plural? If not, delete it or reconsider the wording. Then check words ending in s: some need an apostrophe to show possession, some are ordinary plurals, and some are contractions.
When one style permits more than one possessive form, consistency matters. Purdue notes that adding apostrophe plus s to a singular noun ending in s is common in several academic styles, while some other style guidance omits the added s. Follow the style required for your writing, and make sure your reader can tell a plural from a possessive. [1]
