ACT Grammar Rules: What the English Section Actually Tests

The ACT English section rewards students who know a short, predictable list of ACT grammar rules. It is not about memorizing every term in a textbook. The same handful of concepts, commas, semicolons, apostrophes, agreement, pronouns, modifiers, parallelism, and concision, show up again and again. On the enhanced ACT (2025), English is 50 questions in 35 minutes, so you have a little under a minute per question. Learning these rules cold means you spend that time deciding, not guessing. This guide walks through each rule with quick, practical examples you can apply on test day.

How the ACT English section works

Before the rules, know the format. The enhanced ACT English section gives you 50 questions in 35 minutes, scored on the 1 to 36 scale. English, Math, and Reading are averaged into your composite (Science is now optional and reported separately, and Writing is optional too).

Most questions show you a short passage with underlined portions. You pick the answer that makes the sentence correct and clear, or choose NO CHANGE when it is already right. A few strategy habits help across every question:

• Read the whole sentence, not just the underlined words. Errors often depend on context earlier or later.
• Shorter is often better. When answer choices say the same thing, the ACT usually rewards the most concise, clear version.
• Trust your ear, then confirm with a rule. If something sounds off, name the rule that explains why.

Commas: the rule the ACT tests most

Commas appear constantly, and the ACT wants precise use, not comma-by-feel. Learn these four jobs:

• Joining with a conjunction: use a comma before and, but, or, so when it connects two complete sentences. The lab closed early, so we finished at home.
• After an introductory phrase: After the storm, the game resumed.
• Around nonessential information: if you can remove it and the sentence still makes sense, set it off with commas. My coach, a former sprinter, timed every lap.
• In a list of three or more: We packed pencils, an ID, and a calculator.

Just as important: do not put a comma between a subject and its verb, and never use a comma alone to join two full sentences (that is a comma splice). Wrong: The bus was late, we still made it. Fix it with a period, a semicolon, or a conjunction.

Semicolons, colons, and dashes

These punctuation marks are easy points once you know their one main job each.

• Semicolon: joins two complete, closely related sentences. It works like a period. The results were clear; the team celebrated. A quick test: if you can replace the semicolon with a period, it is probably correct.
• Colon: introduces a list, explanation, or example, and the words before the colon must form a complete sentence. She brought three things: a ticket, an ID, and a calculator.
• Dash: can set off an interruption much like commas or parentheses, or introduce a summary. If a dash opens an aside, a matching dash usually closes it.

A common ACT trap pairs a semicolon with a fragment. If one side is not a full sentence, the semicolon is wrong, and a comma or colon is likely the fix.

Apostrophes and agreement

Two rules here quietly decide a lot of questions.

Apostrophes show possession or contraction, never a plain plural. Watch the classic mix-ups:

• Its = belonging to it. It's = it is.
• Their = belonging to them. They're = they are. There = a place.
• Singular possessive adds 's (the student's desk); plural possessive usually adds just an apostrophe (the students' desks).

Subject-verb agreement: the verb must match its true subject in number. The ACT hides the subject behind extra words. The box of tools is heavy (the subject is box, not tools). Cross out the phrase between the subject and verb to hear the match clearly.

Pronouns, modifiers, and parallelism

Pronouns must agree with what they replace and point to it clearly. If a pronoun could refer to two nouns, the sentence is ambiguous and the ACT will offer a clearer rewrite. Also match number: a singular noun takes a singular pronoun. Each player brought his or her gear, not their in strict usage the ACT tends to test.

Modifiers should sit next to the word they describe. A misplaced or dangling modifier creates a sentence that technically says the wrong thing. Wrong: Running late, the bus was missed. The bus was not running late; you were. Fix: Running late, I missed the bus. When a sentence opens with a describing phrase, the noun right after the comma must be the thing being described.

Parallelism means items in a list or comparison share the same grammatical form. Wrong: She likes reading, to hike, and biked. Right: She likes reading, hiking, and biking. Check any list, pairing, or comparison for matching structure.

Concision and word choice

A large share of ACT English questions are not about a broken rule at all. They ask which correct option is clearest and shortest. The ACT dislikes redundancy and filler.

• Cut repetition: at 8 a.m. in the morning should be at 8 a.m.
• Cut wordiness: due to the fact that becomes because.
• When two answers mean the same thing and both are grammatical, the shorter one is usually right.

Also watch commonly confused words the ACT likes: then (time) vs than (comparison), affect (usually a verb) vs effect (usually a noun), and fewer (countable) vs less (uncountable). Transitions matter too: make sure a word like however or therefore actually matches the logic between the two sentences.

Practice these rules for free on Prep36

Grammar rules stick when you apply them under a timer, not when you only read about them. The best next step is repetition: do a set of questions, miss a few, read the explanation, and try again the next day.

Prep36 gives you 1,000+ original practice questions (these are Prep36 practice questions, not real or official ACT questions; official tests live at act.org), 6 full timed tests, instant explanations, word banks, a daily challenge, and a study planner. The whole question bank is free, with optional Plus at 14 dollars per month and Max at 30 dollars per month if you want more. When you register for the real thing, always confirm current dates and fees at act.org. Start a free English set on Prep36 today and turn these rules into reflexes.

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