# SAT punctuation rules: a sentence-structure checklist Source: https://1600.now/blog/sat-punctuation-rules --- SAT Writing Review SAT sentence boundaries, commas, dashes, colons, apostrophes, and punctuation traps with exact examples and a structural checklist. Written by [Luke Finigan](https://1600.now/about) 5 min read Updated Oct 2, 2026 Choose punctuation from the sentence’s structure: complete clauses need a boundary, interruptions need matching marks, and possessives need the right apostrophe. Do not choose a mark simply where your voice pauses. ### Start with boundaries, not a list of symbols A punctuation choice may change only one character, but that character tells the reader how the sentence is built. First find the main subject and verb. Then decide whether the blank sits between independent clauses, inside a phrase, or around extra information. "The exhibit opened; visitors arrived" contains two complete clauses. "After the exhibit opened, visitors arrived" begins with a dependent clause. The first example needs a boundary joining or separating sentences; the second uses a comma after the introductory clause. Both can sound like a pause, so sound alone cannot distinguish them. If the wording changes with the punctuation, evaluate the whole option. "And" and "however" do not function the same way, and a changed verb may turn a phrase into a clause. Boundaries (Punctuation and Sentence Structure) · Easy The museum catalog identifies the portrait's subject as ______ Mara Solis, whose maps of desert trade routes are on display. A cartographer, B cartographer; C cartographer: D cartographer - [Open the question and explanation](https://1600.now/bank/reading/b3e62021) - [Practice boundaries (punctuation and sentence structure) questions](https://1600.now/bank/reading/skill/Boundaries) - [Print the boundaries (punctuation and sentence structure) worksheet](https://1600.now/sat-boundaries-punctuation-worksheet) ### Keep a compact rule sheet Use this table as a reminder after you understand the examples. The rule is the reason for the mark, not a visual pattern to copy blindly. | Mark or pattern | Job | Example | | --- | --- | --- | | Period | Separates complete sentences | The gate opened. The crowd entered. | | Semicolon | Joins independent clauses | The gate opened; the crowd entered. | | Comma + coordinating conjunction | Joins independent clauses | The gate opened, and the crowd entered. | | Colon | Introduces an explanation or list after a complete clause | They carried two tools: a ruler and a compass. | | Paired commas or dashes | Encloses nonessential information | The instrument, built in 1920, still works. | | Apostrophe | Marks possession or contraction | The researcher’s notes; it’s ready. | ### Commas are not general-purpose pauses Do not place a comma between a subject and verb: "The paintings in the upstairs gallery attract visitors." The length of "paintings in the upstairs gallery" does not create a boundary before "attract." Do not split a verb from its object: "The curator selected three photographs." A colon after "selected" would also break that unit. The complete setup "The curator selected three works: two photographs and a drawing" can take a colon because the object is already present. Use commas for an introductory phrase when the structure calls for it: "After the final rehearsal, the musicians rested." In a series, separate parallel items: "The folder contained letters, maps, and receipts." Coordinate adjectives can take a comma when they independently modify the noun, as in "a careful, detailed report"; do not insert one automatically into every pair of adjectives. ### Check both ends of an interruption "The river, which crosses two counties, floods each spring" encloses a nonessential clause with commas. Removing it leaves "The river floods each spring." If the sentence uses a dash to open that kind of interruption, it needs a matching dash where the main sentence resumes. A single dash can introduce an explanation at the end: "The team needed one thing—a reliable measurement." That is different from an interruption in the middle. The rule is not that every dash must come in a pair. Restrictive information identifies which thing is meant: "The river that crosses the western county floods each spring." Removing the identifying clause can change the intended reference. Do not add paired commas simply because you see "that" or "which"; judge whether the information is essential in the sentence. Semicolons can also divide complex list items with internal commas: "They visited Portland, Oregon; Reno, Nevada; and Tucson, Arizona." These items need not be complete clauses. ### Apostrophes require the owner and number For one researcher, write "the researcher's notes." For multiple researchers, write "the researchers' notes." For an irregular plural without a final -s, place the apostrophe before the possessive -s: "the children's drawings." A plural alone needs no apostrophe: "The researchers arrived." Ask whether the noun owns something or merely names more than one thing. An apostrophe is not a decoration for a plural ending. "Its" is possessive: "The telescope lost its cover." "It's" means "it is" or "it has": "It's been repaired." Replace the word with the expanded phrase to check it. Apply the same test to "who's" versus "whose" and "they're" versus "their." Contractions and possessives can look similar while doing different grammatical jobs. ### Resolve choices in a fixed order Find the main clause, test whether the text after the blank is another independent clause, and identify any conjunction or transition. Then inspect interruptions, lists, and possessives if those are the structures being tested. Read the full completed sentence once before moving on. If you selected a comma splice, rewrite it with a period, semicolon, or comma plus a suitable coordinating conjunction. If you mismatched an interruption, mark where the main sentence stops and resumes. If you missed an apostrophe, name the owner and whether it is singular or plural. Use a Boundaries set in the [SAT question bank](https://1600.now/bank), then follow [commas, semicolons, and colons](https://1600.now/blog/sat-grammar-commas-semicolons-colons) for deeper clause examples. Keep review focused on the structure you missed. Repeating a rule sheet is less informative than explaining why a specific tempting mark fails in a specific sentence. Try it yourself Which sentence has correct possession? A The two researchers' notes agreed. B The two researcher's notes agreed. C The two researchers notes' agreed. ### Sources - [College Board: Reading and Writing question types](https://satsuite.collegeboard.org/practice/student-question-bank/reading-writing) Luke Finigan is a student developer and the creator of 1600.now, a free Digital SAT practice platform. [About Luke](https://1600.now/about). ### Keep reading - **[SAT commas, semicolons, and colons: the clause test](https://1600.now/blog/sat-grammar-commas-semicolons-colons)** Choose SAT punctuation by identifying complete clauses, conjunctions, and explanations, with worked examples and comma-splice checks. - **[SAT subject-verb agreement: find the subject that controls the verb](https://1600.now/blog/sat-subject-verb-agreement)** Check SAT subject-verb agreement through intervening phrases, inverted sentences, compound subjects, and relative clauses. [Browse SAT resources →](https://1600.now/sat-resources)