One for All SAT › SAT notes › Standard English Conventions › Boundaries
Boundaries: SAT Reading and Writing notes
Boundaries questions ask you to pick the right punctuation, or no punctuation at all, at the point where two parts of a sentence meet.
Study it with worked examples and 8 practice questionsPractise Boundaries questions
What this topic tests
A Boundaries question gives you a sentence with a blank, and all four choices use the same words. The only thing that changes is the punctuation: a period, semicolon, colon, comma, dash, parenthesis, or nothing at all. Your job is to work out what kind of pieces sit on each side of the blank, and then use the mark that the rules allow between those two pieces.
The most useful skill here is telling a complete sentence apart from a piece of one. A complete sentence (an independent clause) has a subject and a verb and makes sense on its own. A dependent clause, such as one starting with although or which, or a phrase with no verb of its own, can’t stand alone. Once you can sort the pieces, most questions come down to a short list of rules.
Read the whole sentence, not just the words next to the blank. The clue you need is often a few words away: a dash that opened an aside, a semicolon already used in a list, or the real main verb further along.
Nearly every question falls into one of four situations: two clauses meeting, extra information being set off, places where no mark belongs, and colons and lists. A few rare questions (3 of 84) ask whether a sentence ends with a question mark or a period. Use a question mark only for a direct question in question word order, like “Where did the word come from?” A sentence that just reports a question, like “he was hired to find out how much sweetener most people prefer”, ends with a period.
Key ideas
- A complete sentence has a subject and a verb and can stand on its own. Words like although, because, while, when and which make a clause dependent, so it can’t stand alone.
- You can join two complete sentences in only three ways: a period, a semicolon, or a comma plus a joining word (for, and, nor, but, or, yet, so). A comma alone is a comma splice, and no mark at all is a run-on.
- Words like however, though, rather and therefore are not joining words. When one sits between two complete sentences, you still need a period or semicolon at the break, with a comma on the word’s other side.
- A semicolon has two jobs only: joining two complete sentences, and separating list items that already contain commas.
- A colon must come after a complete sentence. It introduces a list, an explanation, or an example of something the first part set up.
- Extra information in the middle of a sentence needs a matching pair of marks: two commas, two dashes, or two parentheses. Close with the same mark that opened it.
- Essential words get no marks. Never put a single mark between a subject and its verb, a verb and its object, a preposition and its object, or a title and the name right after it.
- Don’t punctuate by ear. Pausing when you read aloud does not mean a comma belongs there.
The 4 kinds of Boundaries question
Sorted from every Boundaries question in the site's bank: each kind keeps coming up, and has a method that works every time.
1. Where two clauses meet
How to spot it. The blank sits right where one idea ends and another idea, with its own subject and verb, begins. The choices swap a period, a semicolon, a comma, a comma plus and or but, or nothing. In a harder version, every choice contains the same word, such as however, though or rather, and only the position of the semicolon changes.
How to answer it:
- Split the sentence at the blank and read each side by itself.
- Ask whether each side could be a complete sentence. If a side starts with a word like although, while or because, or has no main verb, it can’t stand alone.
- If both sides are complete, use a period, a semicolon, or a comma with and, but or so. Cross out any choice that has only a comma or nothing at all.
- If one side can’t stand alone, use a comma (or nothing). A period or semicolon would leave a fragment.
- If a word like however or though appears in every choice, decide by meaning which clause it belongs to. Put the period or semicolon at the real break between the two clauses, and a comma on the word’s other side.
The trap. The comma splice is the big one. A comma feels right because you would pause there, but a comma on its own can never hold two complete sentences together. The second trap is putting the semicolon on the wrong side of however or though. These words aren’t joining words, so check which clause they logically belong to before you choose.
2. Extra information
How to spot it. Part of the sentence adds a description, a side comment, an example, or a which clause that you could lift out and still have a working sentence. Often one mark (a comma, a dash, or an opening parenthesis) is already in the sentence before the blank, and you have to choose how to close it or how to attach the extra part to the main clause.
How to answer it:
- Find the main sentence: its subject and its main verb.
- Find the extra chunk and cover it with your finger. If the sentence still makes sense and says the same main thing, the chunk is extra.
- If the chunk is in the middle of the sentence, it needs a matching pair of marks around it. Look back to see what opened it (a comma, a dash, or a parenthesis) and close it with the same mark.
- If the chunk is at the start or the end, one comma between it and the main clause usually does the job. A period or semicolon is wrong here, because the chunk can’t stand alone as a sentence.
The trap. Mixing marks, such as opening an aside with a dash and closing it with a comma, or forgetting the closing mark altogether. Watch out for commas inside the aside too. They belong to the aside, so they don’t tell you which mark should close it.
3. No punctuation needed
How to spot it. One choice has no punctuation at all, and the blank falls between words that belong tightly together: a subject and its verb, a verb and the thing it acts on, a word like of, from or during and its object, a title and the name it labels, or a noun and a that clause telling you which one you mean.
How to answer it:
- Name the piece on each side of the blank. Is it a subject and then its verb? A verb and then its object? A preposition and then its object?
- If the two pieces work as one unit, no single mark can come between them.
- For a name after a title, or a that clause after a noun, cover it up. If the sentence no longer makes sense or loses who or what it means, the words are essential and get no commas.
- Choose the choice with no punctuation, then reread the whole sentence to check that it flows.
The trap. Adding a comma because the subject is long, or because you’d pause there when reading aloud. A long subject still runs straight into its verb. Also remember that a colon never comes right after a verb or a preposition, even when a list follows.
4. Colons, lists, and series
How to spot it. The sentence contains a list, or a complete clause that sets up something to come (a list, an explanation, or the answer to “what?”). The choices swap colons, semicolons and commas just before or inside the list.
How to answer it:
- Look for a list and check how the items already in the sentence are separated.
- If the items are simple and have no commas inside them, separate them with commas.
- If any item already contains commas, separate the items with semicolons. Copy whatever mark the sentence already uses between items.
- To introduce a list or an explanation, use a colon, but only if everything before it is a complete sentence.
The trap. Using a semicolon to introduce a list. A semicolon joins two complete sentences or separates items in a complex list; it never announces what’s coming next. That’s the colon’s job.
Practise Boundaries
On One for All SAT every question has a step-by-step solution, and the notes have worked examples of each kind of question, then practice questions you can check as you go. It's free, and there's nothing to sign up for.