Grammar Rules for Writing

TL;DR

The PSAT Reading and Writing section (54 questions, 64 minutes, two modules) tests a predictable set of grammar rules. You will see the same error types repeatedly: subject-verb agreement, pronoun clarity, punctuation between clauses, parallel structure, and word choice. Learning to recognize these patterns—not just memorize definitions—is what improves your score.

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Why This Matters

Every grammar question on the PSAT falls into a small number of categories. When you understand the underlying rules, you stop guessing based on what "sounds right" and start identifying exactly what the question is testing. The test hides errors in predictable ways: prepositional phrases that separate subjects from verbs, pronouns with unclear antecedents, and clauses joined with the wrong punctuation.

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Agreement Rules

Agreement errors are among the most common question types. The core principle: words that refer to each other must match in number.

Subject-Verb Agreement

• Singular subjects take singular verbs; plural subjects take plural verbs. The PSAT buries the subject under prepositional phrases—"The collection of rare books is valuable" (not are).
• Collective nouns (team, committee, group) are typically singular when acting as one unit—"The jury has reached a verdict."
• Indefinite pronouns such as everyone, each, nobody, and anyone are always singular.

Pronoun-Antecedent Agreement

• Pronouns must match their antecedents in number. If the antecedent is singular, the pronoun must be singular.
• Ambiguous pronoun reference is a major trap. If "it" or "they" could refer to more than one noun, the sentence needs revision.
• Place pronouns close to their antecedents. Distance creates confusion and signals an error.

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Sentence Boundaries and Punctuation

Punctuation questions test one skill: do you know where one independent clause ends and another begins?

Comma Usage

• Use a comma after introductory elements—"After the storm, we surveyed the damage."
• Non-essential information gets commas on both sides—"My brother, who lives in Texas, visited last week." If the information is essential to meaning, omit the commas.
• Never join two independent clauses with only a comma. This creates a comma splice, one of the most frequently tested errors.

Semicolon and Colon Usage

• Semicolons connect two independent clauses without a conjunction—"I studied hard; I passed the exam." Both sides must be complete sentences.
• Colons introduce lists, explanations, or elaborations, but the clause before the colon must be a complete sentence.
• Semicolons can separate complex list items when items already contain commas—"Paris, France; London, England; and Tokyo, Japan."

Fragments and Run-Ons

• Fragments lack a subject, a verb, or a complete thought—"Because she was tired" needs an independent clause to complete it.
• Run-on sentences jam independent clauses together without proper punctuation. Fix with a period, a semicolon, or a comma plus a coordinating conjunction.
• Length does not equal completeness. A long phrase can still be a fragment; always check for subject + verb + complete thought.

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Verb Tense and Voice

Tense questions test whether the timeline stays consistent. The rule: do not shift tenses unless the meaning requires it.

Verb Tense Consistency

• Maintain the same tense within a sentence or passage unless time shifts—"She walked to the store and buys milk" incorrectly mixes past and present.
• Past perfect (had + past participle) shows an action completed before another past action—"She had finished before he arrived."
• Context clues like "yesterday" or "every day" signal which tense is correct.

Active vs. Passive Voice

• Active voice places the subject as the doer—"The scientist conducted the experiment."
• Passive voice removes the actor and is often flagged as wordy—"The experiment was conducted."
• Passive is not always wrong, but prefer active voice unless the receiver of the action is more important than the doer.

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Sentence Structure and Clarity

These rules ensure sentences are logically constructed and unambiguous.

Parallel Structure

• Items in a list or series must use the same grammatical form—"She likes hiking, swimming, and to bike" breaks parallelism; correct to "hiking, swimming, and biking."
• Parallelism applies to comparisons too—"Running a marathon is harder than to sprint" should be "harder than sprinting."

Modifier Placement

• Modifiers must sit next to what they modify—"Covered in chocolate, I ate the strawberries" suggests you are covered in chocolate.
• Misplaced modifiers create unintended meanings. "She almost drove her car for six hours" vs. "She drove her car for almost six hours" mean different things.
• Dangling modifiers occur when the intended subject is missing entirely—"Walking to school, the rain started" (who was walking?).

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Word Choice and Conventions

Commonly Confused Words

• Their/there/they're—possessive, location, contraction of "they are."
• Its/it's—possessive pronoun vs. contraction of "it is." Possessive pronouns never use apostrophes (his, hers, its, theirs).
• Effect/affect—effect is usually a noun; affect is usually a verb.

Apostrophe Usage

• Apostrophes show possession—singular nouns add 's (the dog's bone); plural nouns ending in s add only an apostrophe (the dogs' bones).
• Contractions use apostrophes to mark missing letters—can't, won't, it's, they're.
• Plural nouns do not need apostrophes—"The Smiths are here," not "The Smith's are here."

Comparative and Superlative Adjectives

• Comparatives compare two items and typically end in -er or use "more"—taller, more interesting.
• Superlatives compare three or more and end in -est or use "most"—tallest, most interesting.
• Irregular forms must be memorized—good/better/best, bad/worse/worst.

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Connecting Ideas

Conjunctions and transitions control how ideas relate. The PSAT tests whether you can identify logical relationships and choose the right connector.

Coordinating and Subordinating Conjunctions

• FANBOYS (for, and, nor, but, or, yet, so) join independent clauses of equal weight. Use a comma before them when connecting two complete sentences.
• Subordinating conjunctions (because, although, since, when, if) create dependent clauses that cannot stand alone.
• The relationship must be logical—"She studied hard, so she failed" is illogical; "but" or "yet" would be correct.

Idiomatic Prepositions

• Certain verbs pair with specific prepositions—"different from" (not "different than"), "consist of" (not "consist in").
• There is no universal rule for idiomatic prepositions; they must be memorized.

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Quick Reference Table

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Self-Check Questions

1. What do subject-verb agreement and pronoun-antecedent agreement have in common, and how do their typical error patterns differ on the PSAT?
2. You see a comma between two clauses. What two things must you check to determine if it is a comma splice?
3. Which type of modifier—misplaced or dangling—has a subject somewhere in the sentence, and which is missing the subject entirely?
4. A question asks you to choose between "better" and "best." What information in the sentence determines the correct answer?
5. What three punctuation options can correctly join two independent clauses?