Boundaries
Using correct punctuation to connect clauses, separate non-essential info, and punctuate lists
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Boundaries is the SAT's core punctuation and grammar skill. Every question boils down to one decision: what punctuation belongs at this spot in the sentence?
Why this matters
Boundaries is the highest-frequency grammar skill on the Digital SAT. Most students rely on "what sounds right" and get burned. The test isn't checking your ear — it's checking whether you know five specific punctuation rules. Master those rules and these questions become automatic.
The five patterns
Connecting Independent Clauses
Two complete sentences need to be joined. Your options: period, semicolon, or comma + coordinating conjunction. A comma alone is always wrong here.
›Supplementary Information
Non-essential info is dropped into the middle or end of a sentence. It gets set off with matching punctuation — two commas, two dashes, or parentheses. Mixing them is a common mistake.
›Separating Introductory Element
A word, phrase, or dependent clause appears before the main sentence. A comma separates it from what follows. Short or long — the comma goes there.
›Punctuating Items in a Series
Three or more items in a list need commas between them. The SAT tests whether you place commas correctly — and whether you avoid adding extras where they don't belong.
›No Punctuation Necessary
The sneaky one. Sometimes the sentence is grammatically complete with no added punctuation. The SAT tests whether you can resist the urge to add a comma that isn't needed.
The biggest trap: comma splices disguised as correct answers. Two complete sentences joined by just a comma — no conjunction — is always wrong on the SAT. If both sides of the comma can stand alone, you need a semicolon, a period, or a comma plus a conjunction like "and" or "but."