19 ACT Grammar Rules You Need to Know to Get a Great Score

For a top-notch ACT English score, you need to know your grammar rules inside and out. More than half of the questions in the ACT English section test your understanding of English grammar, known on the ACT as “Conventions of Standard English” questions.

Although this post won’t go through ALL the English rules to know for the ACT, we will discuss the most commonly tested rules to help you kickstart your ACT grammar practice. Master the following 19 grammar rules, and you’ll not only be better prepared to take on the ACT English questions, but you’ll also have a leg up on the ACT essay (the optional Writing test). Make sure to use our Comprehension Checks and ACT Grammar Practice Questions to test your understanding along the way!

Table of Contents

• Sentence Structure
• Run-On Sentences
• Verbs
• Pronouns
• Conjunctions
• Parallelism
• Modifiers
• Appositives
• More ACT Grammar Practice

Sentence Structure

The basic objective of grammar is to create sentences! Knowing how sentences are structured and how to identify improperly structured sentences should be the first thing you focus on in your ACT grammar practice.

ACT Grammar Rule #1: A Complete Sentence Needs a Subject and a Predicate.

In the sentence “Susie loves fancy snacks,” Susie is the subject (who or what the sentence is about) and loves fancy snacks is the predicate (a phrase that has a verb and a complete thought).

If a sentence doesn’t have these two components, it is called a fragment. Here are a few examples of fragments:

• Jumped over the fence
• I am
• Without a dream to hold on to
• Such as chocolate-dipped strawberries

Comprehension Check:

Why are the above fragments not considered complete sentences?

How to fix a fragment

Knowing how to fix fragments is key for ACT English grammar questions. Most times, fragments can be fixed by…

• Adding the subject: The dog jumped over the fence.
• Adding the predicate: I am like a drifter.

or combining it with another sentence:

• I am like a drifter without a dream to hold on to.
• Susie loves fancy snacks, such as chocolate-dipped strawberries.

 
ACT Grammar Pro Tip:

One of our biggest ACT grammar tips is to watch out for fragments that seem to be connected to the previous sentence, but can’t stand alone grammatically. For example:

She was a wonderful professor. The most wonderful professor.

The second sentence does not have a subject or a complete predicate. An acceptable edit of the sentence would be:

She was a wonderful professor. In fact, she was the most wonderful professor.

Fixing tricky fragments

Many fragment questions on the ACT refer to what look like complete sentences but are actually just two or more fragments connected to each other. In these cases, adding or combining sentence elements might not be enough; you might need to change an element altogether.

Finishing his lab experiment before the rest of the class, then deciding to leave early.

Why is this an incomplete sentence? Because it lacks a subject and a proper verb. To fix it, you would need to add a subject and change the verb form:

Finishing his lab experiment before the rest of the class, Jack decided to leave early.
 

ACT Grammar Pro Tip:

The use of gerunds and the pronoun “he” in the above sentence tricks you into thinking that there is a subject and a verb. A gerund looks like a verb, but it’s actually a derivative of a verb that functions as a noun, sometimes called a helping verb (such as, “She is running.”). Rest assured, you do not need to memorize the definition of “gerund” for the ACT! However, do make sure you can differentiate between verbs and nouns that appear in passages on the exam. The ACT will try to trick you with gerunds, so watch out!

ACT grammar practice: Sentence fragments

Run-On Sentences

In order to understand run-on sentences, it’s important to understand the difference between independent clauses and dependent clauses. An independent clause is a phrase that can stand alone as a sentence. A dependent clause is a phrase that contains a verb but cannot stand alone as a sentence.

Comprehension Check:

What are the independent and dependent clauses in the following?

I enjoyed my night alone despite initially wanting to see a movie with friends.

ACT Grammar Rule #2: A Comma Splice Improperly Combines One or More Independent Clauses.

A run-on sentence is when a sentence has too many independent clauses that aren’t combined properly. Students frequently make the mistake of attempting to combine run-on sentences with a comma, and this results in a grammatical error known as the comma splice.

The following is an example of a comma splice:

I run five miles along the river on Saturdays, I do this even when it’s raining.

Knowing how to identify a comma splice and fix it is critical for your ACT grammar prep. You can fix a comma splice by:

1. Turning the clauses into two separate sentences → I run five miles along the river on Saturdays. I do this even when it’s raining.
2. Using a coordinating conjunction → I run five miles along the river on Saturdays, and I do this even when it’s raining.
3. Using a semi-colon → I run five miles along the river on Saturdays; I do this even when it’s raining.
4. Making one clause dependent: → I run five miles along the river on Saturdays, even when it’s raining.

For more on comma rules and more, be sure to check out this video!

ACT grammar practice: Comma splices

Verbs

Your ACT grammar review needs to include verb tenses and subject-verb agreement. Here are some of the most important rules that will help you with ACT verb questions that you may come across:

ACT Grammar Rule #3: Check for Subject Verb Agreement for Present Tense and “To Be” Verbs

Knowing subject-verb agreement rules, which refers to whether or not the subject matches the corresponding verb, are some of the most useful grammar rules to know for the ACT. In grammar, there are five types of subjects:

• First-person singular (I)
• Second-person singular or plural (you)
• Third-person (or inanimate object) singular (he/she/it)
• First-person plural (we)
• Third-person (or inanimate object) plural (they)

For the present simple and present perfect tenses (more on verb tenses in the next two rules), verb forms are consistent across all subjects except third-person singular verbs and “to be” verbs.

Third-person singular verbs

For third-person singular:

• simple present verbs always end in -s (he likes, she cries, he plays, she fixes)
• present perfect verbs use “has” while all other verbs use “have” (compare He has swum the English Channel before to I have swum the English Channel before).

 
ACT Grammar Pro Tip:

Since the ACT English section requires you to speed through 75 questions in only 45 minutes, don’t waste time checking subject-verb agreement for the following verb tenses:

• simple past
• past perfect
• past perfect progressive
• all basic and progressive future tenses

If these names are confusing, no worries, because we’ll go over them in the next two rules!

The verb forms in these cases are the same across all subjects, including third-person singular (e.g. I walked, he walked, we will walk, she will walk, they had been, he had been).

“To be” verbs

The following are the subject-verb agreement rules for the verb “to be”:

ACT grammar practice: Subject-verb agreement

 
ACT Grammar Pro Tip:

When you come across a question that seems to be testing subject-verb agreement, identify the subject right away and match it with the verb. The ACT will definitely confuse you with sentences like the one above that put information between the subject and the verb. Because “projects” is the word closest to “were,” it looks like there is subject-verb agreement, even though “projects” is not the subject of the sentence; the subject of the sentence is “philosophy.”

ACT Grammar Rule #4: Modals Are Helping Verbs that Define the Mood of Regular Verbs.

Modals are a category of words (auxiliary verbs, also known as helping verbs) that appear before verbs in sentences. These are words like can, should, would, could, may, might, etc. The purpose of modals is to add a subtle distinction to the tone, intent, or purpose of a piece of writing.

Even though you use modals in everyday language, it can be hard to know which situations allow you to use modals interchangeably and which situations require the use of one modal over another.

Take “can” and “could” for example. If you want to ask someone for a favor, you can use the following two options and the meaning is pretty much the same:

Can you pass me the broccoli?
Could you pass me the broccoli?

“Can” and “could” are also used to express possibility but sometimes in different ways. For example, if you’ve been waiting for the bus a while, someone could say the following to you:

The bus can be a little late sometimes → The focus here is on the bus’ past tendency to be late sometimes, which provides information about the present. That’s why “could” does not make sense.

In fact, the bus could be late as much as 20 minutes → The focus here is on the bus’ future possibility of being up to 20 minutes late, based on past information. That’s why “can” does not make sense.

Confusing, right?! Luckily, if you’re a native English speaker, you should know most of these rules internally. So the best way to tackle modals on the ACT is to pay extra attention when they come up.

 
ACT Grammar Pro Tip:

Verbs change to their bare form following modals, meaning that there are no tense or subject-verb agreement markers. ACT English often tests these kinds of minor shifts in verb form, so be on the lookout.

Below are some examples of how verbs change to their bare form when you add a modal:

She is → She should be
They are → They could be
He eats → He might eat

If you’re still unclear on the different ways modals are used, check out the video below, which goes over the above examples in a bit more depth:

ACT grammar practice: Modals

ACT Grammar Rule #5: English Has Six Basic Tenses.

There are two elements that make up the six basic tenses: the tense itself (whether an action happens in the past, present, or future) and the aspect (how an action relates to different aspects of time).

The two main aspects are simple (the focus is on when a singular action is, was, or will be completed) and perfect (the focus is on when an action is connected to more than one time period OR when the action happening is secondary to the action itself).

It’s a bit confusing to discuss aspects without examples, so keep reading! Although you don’t need to memorize these terms for the ACT, being familiar with the general structures of verb tenses will give you an edge on the exam.

Simple past

The simple past tense is used to show something that has already happened → I studied for the ACT last year.

Simple present

The simple present tense is used to express:

• thoughts → He thinks I should get more sleep.
• feelings → I feel better.
• desires → I want the new iPhone. I hope I do well on the ACT.
• facts → A Supreme Court justice’s term lasts a lifetime.
• actions that happen regularly, continuously, and/or unendingly → They go to soccer practice once a week.
• actions or events that are already planned → The guests arrive tomorrow.
• orders or instructions → Turn left at the stop sign.

Simple future

The simple future tense is used to express anything that is intended to happen in the future → I will go to college next year.

Past perfect

The past perfect tense is used to talk about an action in the past that happened before another action in the past → By the time I woke up, my mother had left for work.

Present perfect

The present perfect tense is used to express:

• an action that started in the past and has some relevance to the present → She has played piano for 8 years. They have been to the shoe store twice since it opened.
• a past action in which the focus is more on the action itself rather than the fact that it happened in the past → I have skydived before.

Future perfect

The future perfect tense is used to discuss a completed action in the future → My brother will have turned 30 by the time this decade is over.

ACT grammar practice: Basic tenses

ACT Grammar Rule #6: English Has Six Progressive Tenses.

Progressive tenses describe continuous actions that happen in the past, present, or future. Like basic tenses, they also have simple and perfect aspects.

Past progressive

The past progressive tense is a simple tense used to show something was in the process of happening when something else happened → I was watching TV when you called me.

Present progressive

The present progressive tense is the one we typically use to describe actions taking place in the present → What are you doing right now? I am studying for the ACT, so please don’t bother me.

Present progressive can also be used to describe actions in the future → I am going on vacation tomorrow. They are not working next Monday because it’s a holiday.

Future progressive

The future progressive tense is used to describe an action that is in the middle of happening at a particular time in the future → What will he be doing tomorrow at 11 am? He will be doing his chores.

Past perfect progressive

The past perfect progressive tense is sort of like the past progressive tense but it’s used when you want to stress that an action had been going on for a long time → I had been watching TV for two hours when you called.

Present perfect progressive

The present perfect progressive tense is used to express:

• an action that had been going on in the past and only recently stopped → We are exhausted because we have been studying for the ACT non-stop for four hours.
• an action that started in the past and is happening in the current moment → I have been studying for the ACT for two hours.

Future perfect progressive

The future perfect progressive tense is used to discuss a continuous action in the future at a particular time → My mother will have been making dinner by the time I come home from school.

ACT grammar practice: Progressive tense

ACT Grammar Rule #7: Watch Out for Subjects that Come After the Verb

Subject-verb agreement questions on the ACT also try to confuse you with sentences in which the subject comes after the verb. This is called subject-verb inversion. For example, in the sentence…

Under the lamppost stood a mysterious man.

…the subject “mysterious man” comes after the verb “stood.”

Subject-verb inversions can be particularly tough. When you see a sentence like this, your mental ear has no chance of hearing the correct subject before you get to the verb because you haven’t even read it yet.

ACT Grammar Pro Tip:

In the above sentence, note that there is not a comma after lamppost! Many students want to place a comma here. Resist!

ACT grammar practice: Subject-verb inversion

ACT Grammar Rule #8: Verb Tenses in a Passage Should Be Consistent

Unless there is a specific reason to change the tenses of verbs in a passage (such as a shift from describing past events to describing present or future ones), verb tense should be the same across a passage.

For example, in the sentence, “The noodles are produced on a large automated assembly line and then were put into boxes,” are is in present tense and were is in past tense. The verbs need to be changed to just one tense so that the structure is parallel. If this comes up on the ACT, the verb you choose to change depends on the greater context in the passage.

ACT grammar practice: Verb tense consistency

Pronouns

Pronouns replace or refer to subjects or objects in a sentence. There are several types of pronouns that will come up on the ACT, including:

• Subject pronouns, which replace the subject(s) of a sentence: I / you / he / she / it / we / they
• Object pronouns replace the object(s), or nouns to which an action is being done: me / you / him / her / it / us / them
• Possessive pronouns, which indicate ownership: mine / yours / his / hers / its / ours / theirs

For a full list of pronoun types, check out this list.

ACT Grammar Rule #9: A Pronoun Must Always Match its Antecedent.

An antecedent refers to the subject(s) or object(s) that the pronoun replaces in the sentence/paragraph.

Comprehension Check:

In the below example, does the antecedent match the pronoun?

We went to the store this morning and they were out of milk.

ACT Grammar Pro Tip:

Here are our ACT English grammar tips for knocking antecedent/pronoun questions out of the park:

• “He” or “she” only refers to people. Some people may call their cars/boats/etc “she,” but when it comes to ACT English rules, the correct pronoun is “it.”
• It is perfectly fine to use “one” or “you” when writing about someone else. Yet once you choose which word to use in your writing, you can’t switch back and forth.
• If you see an underlined pronoun with no antecedent in the sentence, the correct answer is just about always the proper noun.

ACT grammar practice: Pronoun-antecedent matching

ACT Grammar Rule #10: Watch Out for Ambiguous Pronouns.

Sentences with two or more antecedents run the risk of having ambiguous pronouns. For example:

Mark met Steve after he had dinner.

Though the writer might know that Mark was the person who had dinner, the reader would have no idea. Here’s the correct way to write the sentence:

Mark met Steve after Mark had dinner.

(A quick aside: Though the sentence above is technically correct and would be a correct answer on the ACT English Test, it isn’t the best way to convey information. If you’re focused on improving the flow of your writing, a better version would be: After Mark had dinner, he met Steve. There, doesn’t that sound better? 🙂 )
 
 

Learn more and practice with ambiguous pronouns!

Conjunctions

Your knowledge of ACT English grammar rules has to include conjunctions because the English section is all about them! The test makers will not only test you on how to use conjunctions correctly but also on how to pick the correct conjunction to convey the intention of a sentence or sentences. Here are the rules about the two types of conjunctions: coordinating and subordinating.

ACT Grammar Rule #11: Coordinating Conjunctions Join Clauses That Are Equally Important.

Coordinating conjunctions describe how two equally important clauses relate to one another: I eat pizza all the time, so I obviously like it. I like pizza, but I don’t like ice cream.

Coordinating conjunctions are also used right before the last item in a list (notice how a comma is used before the conjunction): My favorite things to do at camp are hiking, swimming, and sailing.

The acronym FANBOYS can help us remember coordinating conjunctions: For, And, Nor, But, Or, Yet, So.

ACT grammar practice: Coordinating conjunctions

ACT Grammar Rule #12: Subordinating Conjunctions Join Clauses Where One Clause is the Most Important.

Subordinating conjunctions are used when a sentence has at least one independent clause and one or more additional clauses that enhance the main clause. These clauses can be independent or dependent clauses.

There are many subordinating conjunctions. Here are a few common ones: after, although, because, if, than, that, when, where, while, before, as soon as, since, though, unless, until, once.

Take the following sentence:

I plan to launch my career as a poet once I finish this novel I am writing because my English teacher told me I could do it for extra credit.

In this example above, the main clause is, “I plan to launch my career as a poet.” The subordinating conjunction “once” gives us more information on when the speaker plans to launch her poetic career, and the second subordinating conjunction “because” gives more information on why the writer is writing a novel first. These subordinating conjunctions clearly show how the dependent clauses build on the main clause.

Comprehension Check:

Fill in the blank below. Should it be “because” or “although”?

The first few months have been relatively dry _____ weather forecasters predicted a rainy year.

ACT grammar practice: Subordinating conjunctions

Need more help with conjunctions? Check out this guide from Grammar Monster!

Parallelism

Parallel structure refers to a pattern in writing or grammatical structure. When it comes to sentences that list items, compare two or more items, or contain multiple prepositional phrases, parallelism is key. Because parallelism errors can be some of the hardest to catch, the below rules are some of the most useful grammar rules for the ACT.

ACT Grammar Rule #13: Make Sure That All Items in a List Are Equal.

Do you see anything wrong with the below sentence?

For breakfast, I like to eat cereal, fruit, and I also like yogurt.

“Yogurt” is getting a little extra love there and grammatically-speaking, that’s a no-no.

To correct the parallel structure we need to get rid of the stuff in front of “yogurt” so we just have a list of three nouns:

For breakfast, I like to eat cereal, fruit, and yogurt.

Lists in a sentence don’t necessarily have to be a group of nouns; they could be verb phrases, for example:

To escape the wicked witch, the boy ran out of the gingerbread house, rolled down the hill, and went jumping across a river of fire.

Comprehension Check:

What’s the parallelism error in the above sentence?

ACT grammar practice: Parallelism in lists

ACT Grammar Rule #14: Make Sure the Right Things Are Being Compared in a Sentence

Comparisons are among the trickier parallelism questions tested on the ACT. But once you realize how ridiculous comparison parallelism errors sound to the ear, you’ll be able to spot them with ease.

In the following sentence, we have a parallelism error:

Danny’s test scores weren’t as good as Bryan.

As this sentence stands, it looks like it’s comparing Danny’s test scores to Bryan, the human, which makes no sense. The sentence should read as some sort of variation of the below:

Danny’s test scores weren’t as good as Bryan’s (test) scores.

ACT grammar practice: Parallelism in comparisons

ACT Grammar Rule #15: Isolate Each Phrase in Prepositional Phrases to Ensure Parallelism

Sometimes even trickier parallel structure questions have to do with prepositional phrases, which are—you guessed it!—phrases that contain a preposition. To do well on these types of questions, try reviewing idioms on the ACT, which covers common prepositional phrases.

Comprehension Check:

Below is an example of a sentence with prepositional phrases. How do you think the parallelism in the sentence below can be improved?

I was both surprised and worried about the outcome of our class elections.

ACT grammar practice: Parallelism with prepositional phrases

Modifiers

Modifiers are words or phrases that describe another word or phrase in a sentence. Take the following:

Yawning, Laila got up from the couch and left the room.

In the example, the word “yawning” is modifying the subject, Laila.

ACT Grammar Rule #16: Misplaced Modifiers Describe the Wrong Part of the Sentence

Do you see anything funny in the following sentence?

I don’t get how my sister can walk our dog in heels.

While you may automatically assume that my sister is the one wearing the heels, the sentence makes it seem like the dog is. Although this is surely a delightful mental image, we should eliminate any confusion about who is doing the heel wearing. Here are two ways of doing that:

• Bringing “heels” closer to “my sister”: I don’t get how my sister can wear heels and walk our dog.
• Adding a subordinating conjunction: I don’t get how my sister can walk our dog while wearing heels.

ACT grammar practice: Misplaced modifiers

ACT Grammar Rule #17: Dangling Modifiers Don’t Actually Modify Anything in The Sentence

While a misplaced modifier seems to fit the word or phrase it’s modifying—even though it’s incorrectly placed—dangling modifiers are missing an appropriate word or phrase altogether. Dangling modifiers tend to be easier to catch because they just sound off to the ear.

Take the following sentence for example:

Shoving food into my mouth, a content sigh escaped me.

The sentence currently reads as though the content sigh was shoving food into my mouth, which is just bonkers. To fix this dangling modifier, you need to add in the subject:

Shoving food into my mouth, I sighed contentedly.

ACT grammar practice: Dangling modifiers

Appositives

Appositives are kind of like modifiers, but they are specifically a noun or a noun phrase. The structure of an appositive is a bit different from a modifier as well.

ACT Grammar Rule #18: Most of the Time, Appositives Are Set Off with Commas.

In these scenarios, appositives introduce extra information that is helpful but not essential to the sentence. This means you can lift whatever is set off with commas out of the sentence, and it should still read as a sentence. Take the following sentence with the appositive in italics:

My uncle, the greatest chef who ever lived, is cooking dinner tonight.

You can take the appositive out and the sentence would still be complete:
My uncle is cooking dinner tonight.

So when an appositive is in the middle of a sentence, make sure that one of these commas isn’t dropped and that you’re actually setting off the right part of the sentence with the comma. The following are all incorrect:

• My uncle the greatest chef who ever lived, is cooking dinner tonight.
• My uncle, the greatest chef who ever lived is cooking dinner tonight.
• My uncle the greatest chef, who ever lived, is cooking dinner tonight. (If you take out the part that is set off by the commas, the sentence reads: My uncle the greatest chef is cooking dinner tonight. This is not grammatically correct because there’s still part of the appositive—”the greatest chef“—that’s in the sentence and not correctly separated by commas.)

ACT grammar practice: Non-essential appositives

ACT Grammar Rule #19: Essential Appositives Are Not Set Off with Commas.

This is a trickier scenario that the ACT might test. You can try the “lift it out of the sentence” test to see if taking an appositive out creates an error. Take a look at this example:

President of the school board, Jane Smith, decreed that summer vacation should be abolished.

In this case, if we set Jane Smith off with commas, that would mean it could be lifted out of the sentence and the sentence should still read correctly. But it doesn’t. We would need a “the” before “president” to make this sentence work as it is structured, so Jane Smith should NOT be set off with commas.

(Note that we would no longer have an essential appositive if the sentence was structured like this: Jane Smith, President of the school board, decreed that summer vacation should be abolished.)

Double-check to make sure lift-out method works

For some essential appositive errors, you can’t rely on the lift-out method alone. Take the following sentence for example: Yesterday, I met, my cousin’s partner, Madison.

If you used the lift-out method in this case, you would end up with Yesterday, I met Madison, which is grammatically correct. BUT remember: appositives are kind of like modifiers, as in they’re meant to modify a certain word or phrase. The way that it’s written in the initial sentence, it looks like “my cousin’s partner” is modifying “met,” which does not make sense.

As this sentence is structured, “my cousin’s partner” is an essential appositive; thus, the sentence should read:

Yesterday, I met my cousin’s partner Madison.

ACT grammar practice: Essential appositives

More ACT Grammar Practice

Although this post is a great starting point for prepping for the ACT English section, it definitely does not cover all the ACT grammar rules that will help you score big on test day. For more great ACT English grammar review, definitely check out:

• Everything You Need to Know about ACT Punctuation
• ACT Word Form Rules
• Practice with Usage & Mechanics Questions
• Hard ACT English Problems

Another great tool is the web browser plug-in Grammarly. It’ll check your grammar wherever you’re typing on the internet, giving you an easy way to review your grammar rules without realizing it!

Now that you have all the tools to score big on ACT English, your ACT grammar practice should be a breeze!