The 10 Grammar Rules You Need for the SAT Writing Section

The writing portion of the digital SAT's Reading and Writing section tests a specific set of grammar and usage rules. The good news: it's a short list. You don't need to memorize every grammar rule in the English language. You need to know about ten concepts really well, and you'll be ready for the vast majority of writing questions on the test.

Here are the ten rules that show up most often, with explanations that cut through the jargon.

1. Subject-verb agreement

The subject and verb in a sentence must match in number. Singular subjects take singular verbs, and plural subjects take plural verbs.

This sounds simple, but the SAT makes it tricky by placing words between the subject and the verb. For example:

The collection of rare stamps is valuable.

The subject is "collection" (singular), not "stamps." The phrase "of rare stamps" is just a prepositional phrase sitting between the subject and verb. The SAT loves this pattern.

Strategy: When a subject-verb agreement question comes up, mentally cross out any prepositional phrases or descriptive clauses between the subject and verb. Find the true subject, then match the verb to it.

2. Comma rules

Commas are probably the most-tested punctuation mark on the SAT. Here are the comma situations you need to know:

Use a comma:

• After an introductory phrase: After the concert, we grabbed dinner.
• Before a coordinating conjunction (and, but, or, so, yet) joining two complete sentences: She studied for hours, but she still felt nervous.
• Around non-essential information: My brother, who lives in Chicago, is visiting next week.
• Between items in a list: She packed books, snacks, and a calculator.

Don't use a comma:

• Between a subject and its verb: The dog ~~,~~ ran across the yard. (wrong)
• Before a restrictive clause (information essential to the meaning): Students who study consistently score higher. (no comma before "who")

When you see a comma question, ask yourself: is the information after the comma essential to the sentence's meaning? If removing it changes what the sentence is about, skip the comma. If the sentence still makes complete sense without it, add commas around it.

3. Pronoun clarity and agreement

Pronouns must clearly refer to a specific noun (their antecedent) and agree with it in number.

Agreement: If the noun is singular, the pronoun must be singular. If plural, the pronoun must be plural.

Each student must bring their own calculator. (In standard test English, "each" is singular, so the SAT may test whether you recognize the mismatch, though modern usage accepts "their" as singular in many contexts.)

Clarity: A pronoun should never leave the reader guessing who or what it refers to.

When Sarah met Julia, she was nervous. Who was nervous? This is ambiguous, and the SAT will test whether you can spot it.

Strategy: When you see a pronoun underlined or in the answer choices, trace it back to its antecedent. If there are two possible antecedents, or if the antecedent is missing, the sentence needs to be rewritten with a clearer reference.

4. Parallelism

When a sentence lists items or compares things, those items need to follow the same grammatical structure.

Parallel: She likes running, swimming, and cycling. Not parallel: She likes running, swimming, and to cycle.

The SAT tests this with lists, comparisons, and paired constructions (both/and, either/or, not only/but also).

Strategy: Find the pattern in the first item of a list or comparison, then check that every other item follows the same pattern. If one item breaks the structure, that's your answer.

5. Modifier placement

A modifier (a word or phrase that describes something) needs to be next to the thing it's describing. When it's not, you get a dangling or misplaced modifier.

Wrong: Walking through the park, the trees were beautiful. (This says the trees were walking.) Right: Walking through the park, I noticed the beautiful trees.

The SAT frequently tests this at the beginning of sentences. When a sentence starts with a descriptive phrase followed by a comma, the subject immediately after the comma must be the thing being described.

Strategy: Read the introductory phrase, then check: does the subject right after the comma logically perform or receive that action? If not, the modifier is misplaced.

6. Colon and semicolon usage

These two punctuation marks follow specific rules, and the SAT tests both regularly.

Semicolons connect two complete, independent sentences that are closely related: The test was difficult; many students struggled with the last section.

Both sides of a semicolon must be able to stand alone as complete sentences. If one side isn't a complete sentence, a semicolon is wrong.

Colons introduce a list, explanation, or elaboration. The key rule: what comes before the colon must be a complete sentence. She brought three things: a pencil, a calculator, and her ID. The answer was clear: they needed more time.

Strategy: If you see a semicolon in the answer choices, check both sides. If either side can't stand alone as a sentence, eliminate that choice. For colons, check that the part before the colon is a complete thought.

7. Verb tense consistency

Within a sentence or passage, verb tenses should stay consistent unless there's a clear reason to shift (like a change in time frame).

Inconsistent: She studied all night and then takes the exam in the morning. Consistent: She studied all night and then took the exam in the morning.

The SAT tests this by giving you a passage where most verbs are in one tense, then asking about a verb that breaks the pattern.

Strategy: Look at the surrounding sentences for context. What tense are the other verbs in? Unless the sentence is clearly describing a different time period, match the tense of the verbs around it.

8. Apostrophes

Apostrophes serve two purposes: showing possession and forming contractions. The SAT tests both, and it especially likes to test the difference between possessives and plurals.

Possession:

• Singular: the student's book (one student's book)
• Plural: the students' books (multiple students' books)
• Irregular plural: the children's toys (not childrens')

Contractions:

• it's = it is; its = belonging to it
• they're = they are; their = belonging to them; there = a place
• who's = who is; whose = belonging to whom

Common trap: An apostrophe never makes a word plural. The dog's played in the yard is wrong if you mean multiple dogs were playing.

Strategy: Every time you see an apostrophe, ask: is this showing possession or is it a contraction? If neither, it's probably wrong. For its/it's and similar pairs, expand the contraction and see if the sentence still makes sense.

9. Transition words

The SAT frequently asks you to choose the right transition between sentences or ideas. The key is understanding the logical relationship between what comes before and what comes after.

Contrast (the next idea contradicts or qualifies the previous one): however, nevertheless, on the other hand, despite this, in contrast

Addition (the next idea builds on the previous one): furthermore, moreover, additionally, in addition, similarly

Cause and effect (one idea results from the other): therefore, consequently, as a result, thus, accordingly

Sequence (showing order): first, next, subsequently, finally, meanwhile

Strategy: Before looking at the answer choices, read the sentence before and after the blank. Determine the relationship: does the new sentence agree with, contrast, result from, or follow chronologically from the previous one? Then pick the transition that matches that relationship.

The most common mistake is picking a transition that sounds sophisticated but expresses the wrong relationship. "However" sounds smart, but it's wrong if the next sentence agrees with the previous one.

10. Sentence boundaries (run-ons and fragments)

A run-on sentence happens when two complete sentences are joined without proper punctuation. A fragment is an incomplete sentence.

Run-on: She finished the test she felt relieved. (two sentences with nothing between them) Comma splice (a type of run-on): She finished the test, she felt relieved. (a comma alone can't join two complete sentences) Fragment: Because she finished the test. (starts with "because" but doesn't complete the thought)

Four ways to fix a run-on:

1. Period: She finished the test. She felt relieved.
2. Semicolon: She finished the test; she felt relieved.
3. Comma + conjunction: She finished the test, and she felt relieved.
4. Subordination: After she finished the test, she felt relieved.

Strategy: When you suspect a run-on, try splitting the sentence at the join point. If both parts can stand alone as complete sentences and there's nothing connecting them (or just a comma), it's a run-on. For fragments, check whether the sentence has both a subject and a verb and expresses a complete thought.

How to study these rules

Don't try to memorize all ten at once. Here's a practical approach:

Week 1: Focus on subject-verb agreement, comma rules, and sentence boundaries. These three cover the largest portion of writing questions.

Week 2: Add pronoun clarity, verb tense consistency, and apostrophes. These are straightforward once you know what to look for.

Week 3: Work on parallelism, modifier placement, colon/semicolon usage, and transitions. These tend to be slightly less frequent but still appear regularly.

For each rule, do a set of practice questions focused on that specific concept. When you miss one, identify which of these ten rules was being tested. Over time, you'll start recognizing them instantly.

The pattern behind the questions

Most SAT writing questions follow a predictable structure: the passage uses correct grammar in most places, and one sentence contains an error or could be improved. Your job is to find the version that follows standard conventions.

The test rewards students who know the rules, not students who rely on what "sounds right." English is full of constructions that sound natural in speech but violate standard written conventions. Train yourself to apply the rules rather than trusting your ear.

Ready to test your grammar skills in a timed setting? Browse MockCamp's full-length practice tests and pay attention to your performance on the writing questions. Use the domain breakdown to decide which of these ten rules to review next.