6. Punctuation: Commas, Semicolons, Colons, and Dashes

Punctuation questions on the SAT® focus on whether a punctuation mark correctly reflects the grammatical relationship between the parts of a sentence. The four marks tested most heavily are the comma, semicolon, colon, and em dash.

Comma rules:

• Use a comma + coordinating conjunction (FANBOYS) to join two independent clauses.
• Use commas to set off nonessential (parenthetical) information.
• Use commas in a list of three or more items.
• Comma splice: using only a comma to join two independent clauses is wrong.
• Incorrect: "The experiment failed, the team revised their hypothesis."
• Correct: "The experiment failed, so the team revised their hypothesis."

Semicolons join two closely related independent clauses without a conjunction.

• Correct: "The experiment failed; the team revised their hypothesis."
• A semicolon cannot join a dependent clause to an independent clause.

Colons introduce a list, explanation, or elaboration. The clause before the colon must be a complete independent clause.

• Correct: "She brought three things to the lab: a notebook, a pen, and a ruler."
• Incorrect: "She brought: a notebook, a pen, and a ruler."

Em dashes add emphasis or set off a parenthetical element. They can replace commas, parentheses, or a colon.

• "The answer -- surprising to everyone -- was published the next morning."

Before/After examples:

• Incorrect: "The new policy has one clear goal, to reduce carbon emissions."
• Correct: "The new policy has one clear goal: to reduce carbon emissions."

⚠️ Common mistake: placing a colon after a verb or preposition. The word before a colon must complete a full independent clause.

💡 Tip: if two independent clauses are separated by only a comma with no conjunction, it is always a comma splice -- replace the comma with a semicolon, add a FANBOYS conjunction, or split into two sentences.