The 15 Grammar Rules You Need for ACT English

ACT English is the most predictable section on the test. The same grammar rules get tested over and over. Master these 15 rules and you'll have the foundation to score 30+ on English.

Rule 1: Comma Splices

You cannot join two complete sentences with just a comma.

Wrong: The student studied hard, she got a good score. Right: The student studied hard, and she got a good score. Right: The student studied hard; she got a good score. Right: The student studied hard. She got a good score.

How to fix a comma splice: Add a conjunction (and, but, so), use a semicolon, or make two sentences.

Rule 2: Subject-Verb Agreement

The subject and verb must agree in number. The tricky part is when extra words separate them.

Wrong: The box of chocolates were on the table. Right: The box of chocolates was on the table.

Tip: Cross out prepositional phrases between the subject and verb. "The box ~~of chocolates~~ was on the table." Now it's obvious.

Rule 3: Pronoun-Antecedent Agreement

Pronouns must match their antecedents in number.

Wrong: Each student should bring their textbook. Right: Each student should bring his or her textbook. Also right: Students should bring their textbooks.

Watch for: "each," "every," "anyone," "everyone," "nobody" — these are all singular.

Rule 4: Commas with Nonessential Clauses

Information that can be removed without changing the sentence's meaning gets commas. Essential information does not.

Nonessential (commas): My brother, who lives in Chicago, is visiting. Essential (no commas): Students who study consistently score higher.

Test: Remove the clause. If the sentence still makes sense and keeps its core meaning, use commas.

Rule 5: Apostrophes

• Possessive nouns get apostrophes: the student's book, the teachers' lounge
• It's = "it is." Its = possessive.
• Plural nouns do NOT get apostrophes: the students studied (not student's)

The #1 apostrophe mistake: Confusing "it's" and "its." If you can replace it with "it is," use "it's." Otherwise, "its."

Rule 6: Who vs. Whom

• Who = subject (he/she/they). "Who is calling?"
• Whom = object (him/her/them). "To whom should I send this?"

Quick test: Replace with he/him. If "him" works, use "whom." If "he" works, use "who."

Rule 7: Fewer vs. Less

• Fewer = countable items. "Fewer students"
• Less = uncountable quantities. "Less time"

If you can count it, use "fewer."

Rule 8: Parallel Structure

Items in a list or comparison must be in the same grammatical form.

Wrong: She enjoys running, swimming, and to bike. Right: She enjoys running, swimming, and biking.

Wrong: The test was long, difficult, and took a lot of time. Right: The test was long, difficult, and time-consuming.

Rule 9: Misplaced Modifiers

Modifiers should be next to the word they describe.

Wrong: Walking through the park, the flowers were beautiful. (This says the flowers were walking.)

Right: Walking through the park, she noticed the beautiful flowers.

Tip: If a sentence starts with a descriptive phrase followed by a comma, the subject right after the comma should be the one doing or being described.

Rule 10: Semicolons

Semicolons join two complete sentences that are closely related.

Right: She studied all night; she felt prepared for the test.

Semicolons do NOT:

• Join a sentence and a fragment
• Replace commas in simple lists (unless the list items contain commas)

Rule 11: Colons

Colons introduce a list, explanation, or elaboration after a complete sentence.

Right: She packed three things: a pencil, a calculator, and an eraser. Wrong: She packed: a pencil, a calculator, and an eraser.

The rule: The part before the colon must be a complete sentence on its own.

Rule 12: Conciseness

On the ACT, shorter is usually better. If two answers express the same idea, pick the shorter one.

Wordy: At this point in time, the students were in the process of studying for the test. Concise: The students were studying for the test.

Watch for: "the reason is because" (use "because"), "in order to" (use "to"), "the fact that" (usually deletable).

Rule 13: Redundancy

Don't say the same thing twice.

Redundant: She returned back to school. Better: She returned to school.

Redundant: The tiny, small kitten was cute. Better: The tiny kitten was cute.

Common ACT redundancies: "past history," "true fact," "end result," "each and every," "new innovation."

Rule 14: Transition Words

The ACT tests whether you can pick the right transition:

• Addition: furthermore, moreover, in addition
• Contrast: however, nevertheless, on the other hand
• Cause/effect: therefore, consequently, as a result
• Example: for instance, for example, specifically

Strategy: Read the sentence before and after the transition. Determine the logical relationship, then pick the transition that matches.

Rule 15: Sentence Placement

The ACT will ask "where should this sentence be placed?" Read the paragraph and look for:

• Logical flow — does the new sentence connect to what comes before and after?
• Pronoun references — if the sentence says "this method," it needs to come after a method is mentioned
• Chronological order — events should be in time sequence
• Topic sentences — general statements usually come before specific details

How to Apply These Rules

On the Test

1. Read the entire sentence (not just the underlined part)
2. Identify which rule is being tested
3. Apply the rule
4. If still unsure, pick the most concise option
5. "No change" is correct about 25% of the time — don't be afraid to pick it

In Your Prep

• Learn 2-3 rules per study session
• Practice identifying which rule each question tests
• Keep an error log: which rules do you consistently miss?
• After two weeks of practice, you should recognize rule types instantly

The Conciseness Shortcut

When you're stuck between answer choices on the ACT English section, this heuristic is surprisingly reliable:

1. Eliminate grammatically incorrect options
2. Among the remaining options, pick the shortest one
3. Exception: if the shortest option changes the meaning, pick the next shortest

This works because the ACT heavily penalizes wordiness, redundancy, and unnecessary complexity.

Next Steps

Knowing these rules is step one. Applying them under time pressure is step two. Practice with real ACT-style English questions to build speed and accuracy.

Try our free demo to practice English questions with instant AI feedback that explains exactly which grammar rule was tested — and why your answer was right or wrong. For the full experience with 250+ English questions, check out ClutchACT.