Apostrophes & Possessives: The Little Mark With Big Rules

The apostrophe is a tiny mark with an outsized ability to trip people up. It has exactly two jobs: showing that something belongs to someone (possession) and standing in for missing letters (contractions). It has one famous non-job: it never makes a word plural. Most apostrophe errors come from confusing those roles — especially the its/it's pair, where the rules feel backward.

This guide sorts out singular and plural possessives, the pronoun exceptions, and the plural trap, with worked and practice examples matched to real test difficulty at Northside Tutoring.

Why Apostrophes Matter

Apostrophe questions appear on the SAT Writing module and ACT English, often disguised among similar-looking choices (its/it's, dogs/dog's/dogs'). They reward a clear understanding of possession vs. plural. These finer points sit beyond the SSAT.

The Two Jobs of an Apostrophe

An apostrophe does only two things: it shows possession ("Maria's book") or it marks a contraction where letters are dropped ("can't" = cannot). If a word is neither possessive nor a contraction, it gets no apostrophe.

Singular Possessives

To make a singular noun possessive, add 's — even if the noun already ends in s: "the dog's leash," "the boss's office," "James's car." The 's signals that the next thing belongs to that one owner.

Plural Possessives

For a plural noun that already ends in s, add just an apostrophe after the s: "the dogs' park" (a park belonging to multiple dogs), "the students' projects." For irregular plurals that don't end in s, add 's: "the children's books."

Its vs. It's (and Friends)

Possessive pronouns — its, your, their, whose, our — never take an apostrophe. The apostrophe versions are always contractions:

When NOT to Use One

Never use an apostrophe just to make a word plural. "The 1990s," "two CDs," "the Smiths" — no apostrophes. Writing "apple's $1" or "the Smith's live here" is the error the test wants you to catch. Plural = no apostrophe; possessive or contraction = apostrophe.

Where You'll See This — Test by Test

Apostrophe rules are fixed and tested identically across exams. The SAT Writing module and ACT English test possessives, its/it's, and the plural trap. They go beyond the SSAT.

Watch the Lesson

Sometimes a diagram needs a voice. In the short video below, one of our Northside tutors walks through the core idea and works through test-style problems in real time.

Worked Example Problems

These problems are calibrated to the difficulty you'll actually see on test day. Try each one before opening the solution.

Common Mistakes to Avoid

Practice Problems — You Try

Three problems below. Work each before checking the solution.

The Northside Method — How We Teach This 1-on-1

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