Definition · Plain-language
Apostrophe rules
The apostrophe has exactly two jobs: to mark possession in nouns and to mark missing letters in contractions. It is never used to make a noun plural.
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Possession: the complete set of rules
To show that something belongs to a noun, add 's to a singular noun regardless of its final letter: the dog's collar; James's essay; the bus's route; the company's strategy. For a singular noun ending in s, some style guides permit the apostrophe alone (James'), but adding 's (James's) is the more widely recommended form. For regular plural nouns that already end in s, add only the apostrophe after the s: the students' results; the companies' merger; the dogs' bowls. For irregular plural nouns that do not end in s, add 's: children's rights; women's institute; people's choice; geese's migration. For joint possession, a single apostrophe on the last owner's name indicates shared ownership: "Jack and Jill's house" — one house, two owners. Separate apostrophes indicate individual ownership: "Jack's and Jill's essays" — each has their own.
Contractions: the apostrophe as a placeholder
In a contraction, the apostrophe marks the place where one or more letters have been omitted when two words are merged. Common contractions: it's (it is / it has), you're (you are), they're (they are), we're (we are), don't (do not), won't (will not), can't (cannot), I'll (I will), she'd (she would / she had), could've (could have). The most common apostrophe error is confusing the contraction it's with the possessive pronoun its. The test is simple: try expanding it to "it is" or "it has" — if it reads correctly, use it's; if not, use its. Possessive pronouns (its, his, hers, ours, yours, theirs, whose) never take an apostrophe.
What apostrophes are NOT used for — and the plural error
The apostrophe is never used to form a simple plural. This error, sometimes called the "greengrocer's apostrophe", appears on signs such as "Apple's for sale" and in written text such as "the 1990's" or "two MP's voted". The correct forms are apples, the 1990s, MPs. Apostrophes are also not used for the plurals of numbers (the 1960s), abbreviations (NGOs, PhDs) or capital letters used as words (CDs, DVDs), unless the style guide specifically requires it for readability — some guides permit "dot the i's" to avoid ambiguity, but this is the exception. The single rule that prevents most errors: ask yourself "is this possession or is this a contraction?" If neither, do not use an apostrophe.
Key facts
At a glance
- Possession singular: noun + 's (James's, the dog's, the company's)
- Possession plural ending in s: noun + ' (the students', the dogs')
- Possession plural not ending in s: noun + 's (children's, women's, people's)
- Contractions: apostrophe replaces missing letter(s) (it's = it is; you're = you are)
- Possessive pronouns: never take an apostrophe (its, his, hers, ours, theirs, whose)
- Never for plurals: CDs, 1990s, MPs — no apostrophe
- Most common error: confusing it's (it is) with its (possessive)
Common misconceptions
What people often get wrong
Often heard: You should add 's to make any word plural.
Actually: Apostrophes are never used to make nouns plural. Plurals are formed by adding s or es (or irregular forms): books, boxes, children. The only exception some guides permit is to clarify the plurals of single lower-case letters: "mind your p's and q's".
Often heard: "Its" needs an apostrophe because it is possessive.
Actually: Possessive pronouns — its, his, hers, ours, yours, theirs, whose — never take an apostrophe. The apostrophe in it's is a contraction marker, not a possession marker. "Its" possessive has no apostrophe; "it's" is short for "it is" or "it has".
Often heard: For proper nouns ending in s, you only add an apostrophe, not 's.
Actually: The most widely recommended style (Chicago, Oxford) adds 's to singular nouns ending in s: James's, Thomas's, Dickens's. The apostrophe-only form (James') is used in some journalism styles, but it is not the default in academic or formal writing.
Going deeper
