SAT grammar rules: the punctuation and agreement rules to know

SAT grammar questions test a short list of rules: how to join or separate clauses, how to punctuate extra information, and whether subjects, verbs, and pronouns agree. College Board's Standard English Conventions domain covers these rules and makes up about 26% of the Reading and Writing section, or 11 to 15 questions. Every one asks for the choice that "conforms to the conventions of Standard English," and the rules below decide nearly all of them.

How to spot a grammar question

The question line gives it away. If it asks which choice "conforms to the conventions of Standard English," you're looking at a grammar question. Then compare the choices to see what changes:

Only the punctuation changes. That's a Boundaries question, about where clauses and phrases begin and end.
The verb, pronoun, or noun form changes. That's a Form, Structure, and Sense question, about agreement, tense, and word forms.

Knowing which type you're facing tells you which rule to check.

Punctuation rules

1. Join two complete sentences with a period, a semicolon, or a comma plus a conjunction. A complete sentence, or independent clause, has a subject and a verb and can stand alone. The conjunctions that work with a comma are "and," "but," "or," "nor," "for," "so," and "yet."

Right: The library closed for repairs; it reopened in May.
Right: The library closed for repairs, but it reopened in May.

2. A comma alone can't join two complete sentences. That's a comma splice, and it's always wrong on the SAT.

Wrong: The library closed for repairs, it reopened in May.

3. A semicolon needs a complete sentence on both sides. The one exception is a list whose items already contain commas, where semicolons separate the items.

Wrong: Although the trail was steep; we reached the top.
Right: Although the trail was steep, we reached the top.

4. A colon needs a complete sentence before it. What comes after can be a list, a single word, a phrase, or another sentence that explains the first part.

Right: The recipe needs three things: flour, water, and salt.
Wrong: The recipe needs: flour, water, and salt.

5. "However," "therefore," and "for example" can't join sentences on their own. Between two complete sentences, put a semicolon or period before them and a comma after.

Wrong: The test was short, however, it was difficult.
Right: The test was short; however, it was difficult.

6. Extra information takes a matching pair of marks. If a phrase can be removed without breaking the sentence, set it off with two commas, two dashes, or two parentheses. Don't mix them. A phrase that opens with a comma must close with a comma.

Right: The bridge, which opened last spring, carries two bike lanes.
Wrong: The bridge, which opened last spring carries two bike lanes.

7. Essential information takes no commas. If the phrase tells you which one, it's essential.

Right: The novelist Toni Morrison won the Nobel Prize.
Wrong: The novelist, Toni Morrison, won the Nobel Prize.

8. Never separate a subject from its verb with a single comma, even when the subject is long.

Wrong: The students who finished the project early, presented first.
Right: The students who finished the project early presented first.

The SAT Owl guide to Boundaries questions has worked examples of each punctuation rule.

Agreement and form rules

9. A verb agrees with its true subject, not the nearest noun. Mentally cross out the phrases between the subject and the verb, especially ones starting with "of," "in," "with," or "along with."

Wrong: The box of old letters were found in the attic.
Right: The box of old letters was found in the attic.

Watch for these patterns:

Nouns like "team," "committee," "group," and "company" are singular on the SAT.
Two subjects joined by "and" are plural: "The coach and the captain agree."
"Each" and "every" are singular: "Each of the samples was tested."
When the subject comes after the verb, find it before you choose: "Among the findings were two new species."

10. A pronoun matches the noun it replaces. A singular noun takes "it" or "its." A plural noun takes "they" or "their."

Wrong: The company released their annual report.
Right: The company released its annual report.

Also know the four look-alikes. "Its" is possessive and "it's" means "it is." "Their" is possessive and "they're" means "they are."

11. Verb tense follows the time clues. Look for dates, words like "now," "since," and "last year," and the tense of nearby verbs. Don't switch tenses without a reason.

Wrong: In 1969, the astronauts land on the Moon.
Right: In 1969, the astronauts landed on the Moon.

12. Every sentence needs a main verb. Forms ending in "-ing" and forms starting with "to" can't be the main verb by themselves.

Wrong: The researchers, after years of fieldwork, publishing their results.
Right: The researchers, after years of fieldwork, published their results.

13. A modifier must sit next to what it describes. When a sentence opens with a descriptive phrase, the noun right after the comma must be the one doing the action.

Wrong: Walking into the museum, the paintings amazed the visitors.
Right: Walking into the museum, the visitors were amazed by the paintings.

14. Plurals and possessives are different. Add an apostrophe only when something is owned. "The scientist's notes" means one scientist. "The scientists' notes" means more than one. "The scientists took notes" has no apostrophe because nothing is owned.

The Form, Structure, and Sense guide covers these rules with full SAT-style examples.

A fast method for every grammar question

Read the question line and compare the choices. Name what changes.
For punctuation, find the subject and verb on each side of the blank and decide whether each side could stand alone.
For verbs and pronouns, find the true subject or the noun being replaced.
Apply the rule and reread the whole sentence with your choice in place.

Most grammar questions take less than a minute once you know the rules. That's useful time you can save for the harder reading questions later in the module.

Common traps

The long subject. A long phrase between the subject and the verb tempts you to match the nearest noun.
The "however" splice. A comma before "however" between two complete sentences is still a comma splice.
The half-closed aside. An aside that opens with a comma or dash must close with the same mark.
The extra comma. Don't add a comma without a reason. Every comma needs a job, such as separating list items, setting off an aside, or following an introductory phrase.
The plural pronoun for a group. "The team" and "the city" take "its," not "their."

Practice the rules

Rules stick when you apply them to many questions. Start with the free Boundaries practice questions, then mix in agreement questions until you can name the rule behind every answer.

To see whether grammar is where you're losing points, take SAT Owl's free 24-question diagnostic.