Grammar & Punctuation Reference

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Lists: Use commas between three or more items. The comma before “and” (the serial comma) is required in MLA and APA. We packed water, maps, and snacks.
Two sentences joined by FANBOYS (for, and, nor, but, or, yet, so): put a comma before the joining word. It rained all day, so the game was canceled.
After an introductory word or phrase: After dinner, we read.
Comma splice (wrong): two sentences joined with only a comma. ✗ I finished the essay, it took two hours.✓ I finished the essay. It took two hours. / I finished the essay; it took two hours.
Extra information: set it off with commas. My brother, who is twelve, plays chess.

Semicolon (;) joins two complete sentences that are closely related, without “and” or “but.” The lab ran late; we cleaned up quickly.
Colon (:) introduces a list or explanation after a complete sentence. Bring three things: goggles, gloves, and a notebook.✗ The items are: goggles, gloves, and a notebook.

Possession: one owner, add ’s (the dog’s bowl). Plural owner ending in s, add ’ (the dogs’ bowls). Plural not ending in s, add ’s (the children’s books).
Contractions: it’s = it is. its = belonging to it (no apostrophe). It’s clear the team lost its focus.
Never use an apostrophe to make a plain plural: ✗ apple’s for sale → ✓ apples for sale.

In American English, periods and commas go inside the closing quotation mark: “Let’s go,” she said. In MLA, the period goes after the citation: “the pathway from slavery to freedom” (Douglass 37).

Words	Meaning	Example
their / there / they’re	belonging to them / a place / they are	They’re over there with their books.
your / you’re	belonging to you / you are	You’re forgetting your coat.
to / too / two	direction / also or excess / the number 2	Two of us went to the store, too.
affect / effect	verb: to influence / noun: a result	Sleep affects grades. The effect was large.
then / than	time / comparison	Finish, then rest. She’s taller than me.
who / whom	subject / object (he → who, him → whom)	Who called? To whom did you write?
fewer / less	things you can count / amounts you can't count	fewer mistakes, less time

Fragment: missing a subject or verb, or a dependent clause alone. ✗ Because it was raining. ✓ We stayed in because it was raining.
Run-on: two sentences with no punctuation. ✗ I like math it is fun. ✓ I like math because it is fun.
Subject–verb agreement: The box of crayons is on the table (the subject is box, not crayons).
Capitalize the first word of a sentence, proper nouns (Ohio, Monday, the Civil War), and titles of works.

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