Apostrophes are used to show possession (e.g., 'John's book') and to create contractions (e.g., 'don't' for 'do not'). Understanding when and how to use apostrophes prevents common errors and makes writing clearer.
In texts, identify possessive nouns and contractions. Practice writing both forms and identifying when to use each.
The apostrophe has exactly two jobs in English: marking where letters have been omitted in a contraction, and marking ownership in a possessive noun. Every correct apostrophe you write falls into one of these two categories. If you can't place your apostrophe in one of them, it probably doesn't belong there at all — which rules out the most common error of all: writing "apple's $1.99" on a grocery sign, where the apostrophe marks neither omission nor possession.
Contractions are the simpler case. When two words collapse into one, the apostrophe stands in for the missing letters: "do not" becomes "don't" (the *o* is gone), "it is" becomes "it's" (the *i* is gone), "they are" becomes "they're" (the *a* is gone). Reading the apostrophe as a placeholder for something missing is the key mental move. You already know possessive pronouns from your earlier study — *mine, yours, his, hers, its, ours, theirs* — and crucially, none of them take apostrophes because none of them involve omission. "Its" is already possessive by design, the same way "hers" is. The only time you write "it's" is when you mean "it is" or "it has." The classic test: read your sentence aloud with the expanded form. "The cat licked it's paw" → "The cat licked it is paw" — that's nonsense, so the apostrophe is wrong.
For possessive nouns, the rule is more systematic than it feels. Singular nouns get 's: "the dog's leash," "James's car," "the committee's decision." Plural nouns that already end in *s* get just an apostrophe after: "the dogs' leashes," "the committees' decisions." Plural nouns that don't end in *s* get 's just like singulars: "the children's toys," "the geese's honking." The test for placement is always: what does the noun look like *before* you add anything? Take the base form, add the apostrophe, then add *s* only if the word doesn't already end in one. "The dogs" → "the dogs'" (already ends in *s*, so apostrophe after). "The child" → "the child's" (doesn't end in *s*, so add 's).
The deepest confusion in apostrophe usage comes from conflating two different kinds of "s" endings. A plain plural (three cats, two teachers) and a possessive (the cat's whiskers, the teacher's desk) happen to look almost identical — one is "cats," one is "cat's" — but they do entirely different grammatical work. Plurals say "more than one." Possessives say "this belongs to X." Knowing which job the "s" is doing in your sentence tells you whether the apostrophe belongs there. If your noun is just plural, no apostrophe. If your noun is possessive, apostrophe required. If your noun is a possessive pronoun (its, theirs, whose), no apostrophe ever — the language built the possession in from the start.