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Grammar and Usage Unit 4: Punctuation

Punctuation tells readers how to group ideas. Most tested rules involve commas, semicolons, colons and apostrophes.

Covers: Commas (lists, introductions, nonessential clauses), semicolons, colons, apostrophes, dashes

Study guide

Commas separate and clarify. Use them between three or more items in a list (the final serial comma before "and" is a style choice, but be consistent), after introductory words, phrases and clauses ("After the game, we ate"), before a coordinating conjunction that joins two independent clauses, between coordinate adjectives, and around nonessential information. Nonessential (nonrestrictive) clauses and phrases add extra detail and could be removed without changing the meaning: "My cousin, who lives in Denver, is visiting." Essential clauses that identify which one take no commas: "Students who finished early may leave." Also use commas with direct address, dates, addresses and quotations.

A semicolon joins two closely related independent clauses without a conjunction ("The museum closed; we went home") and can separate list items that already contain commas.

A colon comes after a complete sentence to introduce a list, an explanation or an example: "She packed three things: a map, a flashlight and snacks." Don't use a colon after an incomplete phrase like "such as" or "including."

Apostrophes show possession and form contractions. Singular nouns add 's (the dog's bowl); plural nouns ending in s add just an apostrophe (the dogs' bowls); irregular plurals add 's (the children's toys). Possessive pronouns (its, yours, theirs, whose) never use apostrophes; it's always means "it is."

Dashes set off an interruption or emphasize a point, used in pairs in the middle of a sentence, and they can replace commas, parentheses or colons for emphasis. Hyphens join compound words, like a well-known author.

Use a comma before a short question tagged onto the end of a statement ("You're coming, aren't you?") and before a contrasting element that begins with not ("We wanted answers, not excuses"). An appositive is a noun phrase that renames the noun beside it. If the noun is already identified, the appositive is extra and gets commas: "My mother, Ana, is a nurse" (you have only one mother). If it tells you which one, it gets no commas: "My friend Ana is a nurse" (you have several friends).

In American English, commas and periods go inside closing quotation marks ("I'm ready," she said.), and colons and semicolons go outside. A question mark goes inside only if the quoted words are themselves a question.

Key ideas

• Use commas in lists, after introductory elements, and around nonessential information.
• Don't separate a subject from its verb with a single comma.
• Semicolons join two independent clauses; colons introduce a list or explanation after a complete sentence.
• Apostrophes show possession (the dog's bone) or contractions (it's = it is).
• Dashes set off strong interruptions; use them in pairs mid-sentence.

Formulas and rules

Common mistakes

• Using it's for possession.
• Putting a colon after an incomplete thought ("My favorites are: …").

Words to know

Colon

Follows a complete sentence to introduce a list or explanation.

its vs it's

its = belonging to it; it's = it is.

Plural possessive

Add an apostrophe after the s: the students' books.

Nonessential clause

Extra information set off by commas.

Semicolon

Joins two closely related independent clauses.

Serial (Oxford) comma

The comma before "and" in a list of three or more.

Introductory comma

After an opening word, phrase or clause.

Coordinate adjectives

Adjectives separated by commas: a long, cold winter.

Essential clause

Identifies which one; no commas.

Apostrophe (contraction)

Marks missing letters: don't, it's.

Irregular plural possessive

Add 's: children's.

Dash

Sets off an interruption or adds emphasis.

Hyphen

Joins compound words: well-known.

Colon misuse

Don't use one after "such as" or "including."

Sample practice questions

15 more questions like these, from level 1 to 5, are in the practice set.