An SAT Reading & Writing micro-topic under Form, Structure and Sense (Expression of Ideas + Standard English Conventions). Free to read — no account needed.
An apostrophe marks possession, not a plural. To make a word plural — meaning more than one — you just add -s with no apostrophe: one book becomes two books.
To show that a single owner possesses something, add 's. "The dog's bone" means the bone belonging to one dog. This holds even for words that end in s, like "the boss's office".
When the owner is plural and already ends in s, add just an apostrophe after that s. "The dogs' bones" means the bones belonging to several dogs. For irregular plurals like "children", you still add 's: "the children's toys".
The trickiest pair is its and it's. "Its" is the possessive, meaning "belonging to it", as in "the company changed its logo". "It's" always means "it is" or "it has", so use it only when you could replace it with those words.
Worked examples
Which choice is correct? "After the storm, the two ______ branches were scattered across the yard." (A) tree's (B) trees' There are two trees, so the owner is plural, and a plural owner ending in s takes just an apostrophe. So (B), "trees'", is correct.
Which choice is correct? "The new phone is impressive, but ______ battery drains quickly." (A) its (B) it's The blank shows the battery belonging to the phone, which is possession, not "it is". So (A), "its", is correct.
Which choice is correct? "Only one runner finished, and the ______ time was a new record." (A) runner's (B) runners' There is a single runner who owns the time, so a singular possessive is needed. So (A), "runner's", is correct.
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