ACT English grammar: Everything You Need to Know About Sentences


ACT English grammar: Everything About Sentences

You may think that of all the grammar concepts you will be tested on during the ACT English, the easiest one will be recognizing a proper sentence. However, you may be surprised to find out that your ability to recognize a sentence (vs. a fragment or a run-on) is one of the most commonly-tested rules because it can be very tricky?

The ACT tricks many unsuspecting students with seemingly easy concepts. Do you know what you need in order to have a complete sentence? Can you confidently tell the difference between a subordinate clause and an independent clause? Do you know how to use semicolons and what punctuation is necessary for conjunctive adverbs?

In this guide, we will talk about what makes up a grammatically correct sentence, how prepositional phrases, appositives and relative clauses can make sentences confusing and difficult to understand, how to recognize and correct fragments and run-on sentences, and more.

Test Yourself

ACT English grammar: Everything About Sentences

Read the list of phrases below. Can you recognize which ones are complete sentences, which are fragments, and which are run-ons?

  1. My friend, Kate, collects sea shells on the beach.
  2. Kate, who is friendly and easy-going.
  3. After knowing Kate for 10 years, I met another friend, her name was Nicole.
  4. Nicole, who is more serious than Kate, does not like the beach.
  5. Although she didn’t like the beach, but she loved hiking in the mountains.
  6. Nicole, laughing at Kate’s joke.
  7. Kate would become excited.
  8. Because Kate wanted to spend all of her free time together, Nicole, who would want some privacy.
  9. At first, Kate didn’t understand her, soon learned to enjoy new experiences.


Answers: 1. Sentence; 2. Fragment; 3. Run-On; 4. Sentence; 5. Fragment; 6. Fragment; 7. Sentence; 8. Fragment; 9. Run-on.

What is a Sentence?

ACT English grammar: Everything About Sentences

In English class, you have probably learned that the minimum requirement for a complete sentence is a subject and a verb. More specifically, a complete sentence must have at least one independent clause.

Although the ACT will not test you on any of the grammar terms we discuss here, it is still important to understand these ideas.

Simple Sentence

A simple sentence that consists of one independent clause must have three main features:

  1. a subject (noun – a person or thing doing an action)
  2. a verb that is correctly conjugated to match the noun
  3. must express a complete thought and stand on its own.

In the example above:

My friend, Kate, collects sea shells on the beach.

The subject (person or thing doing the action) is “friend”. The verb, or action word, is “collects.” The verb is correctly conjugated to match the subject of the sentence, my friend. If you took away several of the words, the sentence would still make sense.

My friend collects shells.

Exception to the rule: There are circumstances, when you see a complete and correct sentence, but cannot see the subject. These sentences are direct commands.

Go! Stop! Help! Give me a hand!

Although it’s easy to see the action in these sentences, it’s difficult to identify the subject. As a rule, in commands, the subject is always implied to be “you.” This is because when you give a command, you’re always telling someone else what to do. This is the only time when it’s ok not to have a clear subject. The ACT rarely tests this, but it’s good to know.

Now that you have a good understanding of a simple sentence, let’s talk about sentences that are compound or complex that ACT might use to trick you.

Compound Sentence

A compound sentence is a sentence that has more than one independent clause. This means that it has two subjects and two verbs.

This kind of construction can get tricky and confusing because you have to make sure that the two independent clauses are joined together correctly. If they are joined together by only a comma, they’re called run-on sentences.

There are several ways that can be used to correctly join two independent clauses and make a compound sentence.

Join Independent Clauses with a Comma and a Coordinating Conjunction

ACT English grammar: Everything About Sentences

Coordinating conjunctions you’re most familiar with are FANBOYS: for, and, nor, but, or, yet, so.

Example:         Mickey and Goofy went to the park, and they ate ice cream.

You must always use a comma before a coordinating conjunction when joining two independent clauses.

Join Independent Clauses with a Semicolon

Grammatically, a semicolon is identical to a period. Because of this fact, you can join two sentences with a semicolon and nothing else.

Example:         Mickey and Goofy went to the park; they ate ice cream.

Join Sentences with a Semicolon (or Period) and conjunctive adverb

ACT English grammar: Everything About Sentences

The English language contains several conjunctive adverbs, but the most important ones are: however, therefore, consequently, and moreover.

You can pair one of these words with a semicolon or period to show the relationship between the two joined sentences.

Conjunctive adverbs create three distinct transitions:

Contrasting transitions: However, Nevertheless

Adding transitions: Moreover, Likewise

Cause and effect transitions: Consequently, Therefore, As such

Example:         Mickey and Goofy went to the park; moreover, they ate ice cream.

Remember that when using this construction, you must use a semicolon before and a comma after the conjunctive adverb.

Make One of the Sentences a Dependent Clause

This approach involves many variables and because of this can be the most tricky.

Example:         Because Mickey and Goofy went to the park, they ate ice cream.

Notice that the dependent clause is separated from an independent clause by a comma.

Sometimes, when using this construction, you might need to add one or two words or rearrange words in order to have the sentence make more sense.

Sentences with Dependent Clauses

What is the difference between a dependent and independent clause?

As discussed previously, an independent clause forms either a simple sentence or a part of a composite sentence and can stand on its own. A dependent clause has a subject and a verb but cannot stand on its own and must be attached to an independent clause. If a dependent clause is used on its own, it is called a fragment.

A dependent clause is usually used to explain something about the independent clause that it is attached to. For example, a dependent clause can explain why or where an independent clause is happening or may tell background details about the independent clause.

Dependent clauses always begin with a subordinating conjunction (ex: after, although, because, once, since, unless, until, while, wherever, etc.). The presence of a subordinating conjunction signals that the phrase cannot stand on its own. (Read this article, if you need additional explanation on the usage of subordinating conjunctions and other parts of speech).

Example:         Because I neglected to water them, my plants died.

In this example, “my plants died” is the independent clause. This phrase is able to stand on its own with no further explanation necessary.

In contrast, the dependent clause “because I neglected to water them” gives an explanation for the independent clause that follows, but it does not make sense on its own and makes the reader wonder what happened?

If you encounter a free-standing dependent clause on the ACT, it will always be incorrect.

Sentences with Prepositional Phrases, Appositives, and Relative Clauses

Prepositional Phrases

Prepositional phrases can be used to add more detail about how, where, and by whom something is done. They can be added almost anywhere in a sentence.

A prepositional phrase consists (at a minimum) of a preposition and a noun or pronoun that is called the object of the preposition. Common prepositions include words such as out, in, under, within, except, etc. You can find a list of commonly used prepositions in the English language in this article.

Example:         A strict teacher in that classroom enjoys lecturing students. (prepositional phrase tells where the teacher is).

Example:         A strict teacher enjoys lecturing students in that classroom. (prepositional phrase where the teacher likes to lecture).

Remember: You should be able to delete a prepositional phrase and still have a full sentence. If you don’t, then your sentence is incorrect.

Correct:           A strict teacher enjoys lecturing students.

Similar to a dependent clause, a prepositional phrase cannot stand on its own.

Incorrect:         In that classroom.

Relative Clauses

Relative clauses are used in some sentences to add information. These clauses are not necessary for the sentence to make sense.

Non-essential clauses can begin with a relative pronoun such as that, which, whose, or where and, like any other clause, must include a subject and a verb.

Example:         A strict teacher, who was sitting at his desk and grading papers, thought about summer break.

In this sentence, the subject of a relative clause is “who” and the verb is “was sitting.”

Relative clauses can be completely removed from a sentence and the sentence will still make sense.

Example:         A strict teacher thought about summer break.

Remember: If you remove the relative clause and the remaining sentence doesn’t seem right, you have a fragment.



An appositive is a word or a phrase that adds additional information. It describes the subject of the sentence and can be removed without changing the meaning of the sentence.  Appositives are always offset by commas.

Example:         John Smith, who swam 100 meters in under a minute, won an award for most improved swimmer.

In this sentence, the phrase “who swam 100 meters in under a minute” describes the subject of the sentence “John Smith.”

Removing the appositive does not change the meaning or the point of the sentence:

Example:         John Smith won an award for most improved swimmer.

As before, if after removing an appositive, a non-essential clause, a prepositional phrase, or a relative clause the sentence loses its meaning or structure, you have a fragment.  ACT commonly uses fragments as the trickiest mistake sentences.

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Next Steps

Now that you’ve mastered one of the trickiest concepts on ACT English, check out our articles / videos about fragments and run-ons! Read our articles on how the ACT English will test your knowledge of pronoun agreement, punctuation, wordiness and redundancy.

Need to brush up on the basics? Read about the fundamentals of grammar in our parts of speech article.

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