SAT® · Reading and Writing: Form, Structure, and Sense — Modifiers, Genitives, and Plurals
The Compound Possessive
When two people own one thing together, only the second name gets the apostrophe. When they each own a separate thing, both names get their own apostrophe.
The test checks whether you can tell joint ownership from separate ownership, and punctuate each correctly. Joint ownership means one shared thing: Maria and Luis's apartment is a single flat they both live in, so the phrase gets exactly one apostrophe, placed on the last name. Separate ownership means each person has their own version of the thing: Maria's and Luis's apartments means two different flats, so each name carries its own apostrophe, and the noun usually goes plural to match.
The logic behind the one-apostrophe rule is that the whole phrase 'Maria and Luis' acts as a single unit before the apostrophe lands. Think of 'Maria and Luis' as one combined owner. Mark only the end of that unit, the same way you'd mark the end of any single possessor. If you mark both names, you've accidentally created two separate owners, which only makes sense if the thing owned is also split into separate pieces, one per person.
This connects directly to the ordinary singular-versus-plural possessive check you already run on one noun, like deciding between the dog's leash and the dogs' leashes. With a compound subject, you're doing that same check, but you're asking it about the relationship between two owners instead of about one noun's number. Spot whether the sentence describes one shared item or multiple separate items, then let the apostrophe placement follow from that answer rather than guessing.
Key terms
- Compound possessive
- A possessive construction built from two or more names or nouns sharing a grammatical relationship to the thing owned.
- Joint possession
- Two or more owners sharing a single item, marked by one apostrophe on the last-named owner only.
- Separate possession
- Two or more owners each holding their own distinct item, marked by an apostrophe on every name.
- Possessive apostrophe
- The mark added to a noun to show ownership, placed before the s for singular owners and after for most plural owners.
Watch it explained
- How it worksHow does putting the apostrophe on only the last name signal that the ownership is joint?
- Worked exampleWalk me through punctuating a sentence where two researchers share one lab and hold separate grants.
- Common mistakeWhy doesn't adding an apostrophe to both names always make the sentence safer?
- Ties togetherHow does joint possession connect to the plural-or-possessive test you run on a single noun?
Check yourself
End of topic.