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You may think that of all the grammatical concepts you will encounter on the ACT English, recognizing a correct sentence will be one of the easiest ones. But did you know that this is actually one of the most commonly-tested subjects because it can be very tricky?

Do you know what you need to have in order to have a complete sentence? Can you reliably tell the difference between a subordinate clause and an independent clause? Do you know how to use semicolons and conjunctive adverbs?

Read this guide to see how the ACT manages to trick so many students with this seemingly easy concept.

In this guide I will show you:

• What grammatically constitutes a complete sentence
• How prepositional phrases, appositives and relative clauses can make sentences more difficult to understand
• How to recognize and fix fragments
• How to recognize and fix run-on sentences
• Strategies to attack these kinds of questions
• Examples of this kind of ACT question

Test Yourself

Can you recognize which of the following are correct sentences, and which are fragments and run-ons?

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?

You may have heard in your English class that a sentence needs to have a subject and a verb. More specifically, a correct, complete sentence has to have at least one independent clause.

The ACT will not test you on any of the grammatical terms we cover, but understanding the ideas is important. A simple sentence made of one independent clause has three main characteristics:

1. A subject (a person or thing that is doing an action)

2. A verb that is correctly conjugated to match the noun

3. It expresses a complete thought and makes sense on its own

Let's look at one of the above sentences and see if it matches this description.

My dog, Angel, barks at squirrels in the front yard.

The subject - the person or thing doing the action - is "dog." The verb, or action word, is "barks." The verb is correctly conjugated in the 3rd person singular to match the subject of the sentence, my dog. If you wanted to, you could get rid of the rest of the sentence and it would still technically make sense!

My dog barks.

There are some rare circumstances in which you will see a complete, correct sentence where you cannot as easily pick out the subject: direct commands. 

Stop! Help! Give me an umbrella!

Though you can easily spot the action words in these sentences, it's less clear what the subject is. In commands, the subject is always understood to be "you." This is because you are always telling someone else what to do when you give a command! This is the only time that it's ok to have a sentence without a clear subject. The ACT will rarely test this, but it's good to know just in case.

You now know everything you need to know about simple sentences! But did you know that sentences can also be compound or complex? Let's go over these concepts next to see how the ACT might try to trick you.

Compound Sentences

A compound sentence is a sentence that has more than one independent clause - meaning two subjects and two verbs.

This kind of construction can start to get tricky, because you have to make sure that they're joined together correctly. If they aren't, they're called run-on sentences. We'll discuss these more below. 

There are several different ways that you can join independent clauses together correctly to make a compound sentence.

Join the sentences with a comma and a coordinating conjunction

Coordinating conjunctions are probably the conjunctions you're most familiar with, including and, but, and or. You can remember all of them with the acronym FANBOYS:

As an example, let's look at the following independent clauses:

Ben and Kate always enjoyed eating Chinese food. They began to prefer Japanese food after traveling to Japan.

Here is how you could join these two independent clauses with a coordinating conjunction:

Ben and Kate always enjoyed eating Chinese food, but they began to prefer Japanese food after traveling to Japan.

Remember that when using a coordinating conjunction to join two sentences, you must always use a comma.

Join the sentences with a semicolon

A semicolon is grammatically identical to a period. As such, you can join two sentences with a semicolon and nothing else.

Ben and Kate always enjoyed eating Chinese food; they began to prefer Japanese food after traveling to Japan.

Join the sentences with a semicolon (or period) and conjunctive adverb.

There are several different conjunctive adverbs, but some of the most common ones are: however, nevertheless, therefore, moreover, and consequently.

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

Notice that the different adverbs show different relationships.

However and nevertheless show a contrast.

Therefore and consequently show a cause-and-effect relationship.

Moreover adds emphasis and expand on information.

Ben and Kate always enjoyed eating Chinese food; however, they began to prefer Japanese food after traveling to Japan.

Remember when using this construction that you should always have a comma after the conjunctive adverb.

Make one of the sentences a dependent clause

We will talk more about dependent clauses in a moment, but this is how this tactic would look:

Though Ben and Kate had always enjoyed eating Chinese food, they began to prefer Japanese food after traveling to Japan.

Once again, note that the dependent clause is separated from the main clause by a comma.

You will also often find that you need to add a word or two when using this method in order to have the sentence make more sense, or rearrange the order of the words.

Because of the many variables involved, this approach can be one of the more difficult options for joining two sentences together. 

Let's look more into how dependent clauses are formed and how they are used.

Sentences with Dependent Clauses

So what is the difference between an independent clause and a dependent clause? Unlike independent clauses, which can stand on their own, a dependent clause must be attached to an independent clause.

Though dependent clauses have a subject and verb, they don't make sense on their own.

Instead, a dependent clause is usually used to explain something about the independent clause that it is attached to. The dependent clause may tell background details about the independent clause, or where or why the independent clause is happening.

Dependent clauses will begin with a subordinating conjunction that gives you a signal that it cannot stand on its own. For more on subordinating conjunctions, see this article.

Although he loved his country, he moved abroad to find new opportunities.

In this example, the independent clause is "he moved abroad to find new opportunities." This is able to stand on its own and makes perfect sense without any more information.

In contrast, look at the dependent clause, "Although he loved his country." This gives background information for the independent clause that follows, but it does not make sense on its own. The reader is left wondering what did he do? 

Remember that if you encounter a dependent clause on its own on the ACT, it will always be incorrect. I will discuss this in more detail below in the "Fragments" section.

Sentences with Prepositional Phrases, Appositives, and Relative Clauses

Prepositional Phrases

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

You can find a list of the most common prepositions in the English language in this article. A prepositional phrase consists of (at least) a preposition and a noun that's called the object of the preposition. Let's look at some examples of how these are used:

Remember that you should always be able to completely delete a prepositional phrase and still have a full sentence left over. If you don't, then your sentence is incorrect!

The young man enjoys eating cake. CORRECT 

Like a dependent clause, a prepositional phrase cannot stand alone as a sentence.

In that coffee shop. INCORRECT

Relative Clauses

Some sentences also have relative clauses. These clauses aren't necessary for the sentence to make sense; instead, they add extra information.

Non-essential clauses will begin with a relative pronoun, such as that, which, whose or where. Since they're clauses, they should always include a subject and a verb.

Let's look at an example:

The young man, who was sitting in the cafe and eating cake, dreamed of getting a PhD.

In this sentence, the subject of the relative clause is "who." The verb is "was sitting."

Relative clauses can be completely removed from the sentence and you'll still have a complete sentence left over.

The young man dreamed of getting a PhD.

Note that this means that if you remove the non-essential clause and something doesn't seem right with the remaining sentence, you have a fragment on your hands! I'll discuss this more below.

Appositives

An appositive is a word or phrase that consists of a noun or a pronoun and its modifiers that is placed directly next to another noun or pronoun that it's describing. The point of an appositive is to add more information about a noun in a sentence. 

Appositives should be surrounded by commas.

Jeff, the young man, sat in the cafe and ate cake while he studied.

In this sentence, "the young man" is an appositive fodescribing the noun "Jeff."

As you may have guessed, you should be able to remove an appositive and have a complete sentence left over. 

Jeff sat in the cafe and ate cake while he studied.

But what if you cross out an appositive, prepositional phrase, or non-essential clause, and the sentence you have doesn't seem quite right? Now that we've learned the correct ways to form sentences, let's look at some of the most common mistake sentences you will see on the ACT - fragments.

What Is a Fragment?

A fragment is an incomplete sentence. There are 6 main mistakes that can make a sentence a fragment:

• A “sentence” that lacks a verb
• A “sentence” that has an -ing or non-past tense -ed verb without a helping verb
• A “sentence” that lack a subject
• A “sentence” that begins with a subordinating conjunction and has no main clause
• A “sentence” that adds details to the main clause, but is separated from it
• A “sentence” that has a nonessential clause or prepositional phrase and incomplete main clause

Let's look at each of these individually.

Sentences That Don't Have a Verb

How to recognize these fragments: ask what the subject of the sentence is doing. 

If you can't answer that question, it's most likely because there isn't a verb!

How to fix these fragments: you must add a verb to show an action or a state of being.

Sentences with an -ing verb or non-past tense -ed verb and no helping verb

How to recognize these fragments: whenever you see an “-ing” verb, or an “-ed” verb that doesn’t seem to be describing the past tense, there MUST be a helping verb with it or another verb somewhere else in the sentence. If it has neither, the sentence is a fragment.

There are three ways to fix these fragments: add a helping verb, or change the verb to another form if it's appropriate.

You can also fix this type of fragment by using the -ed or -ing word as a an adjective (called a participle) and adding another verb.

Sentences That Lack a Subject

How to recognize these fragments: ask yourself who is doing the action.

You may notice that some of these examples have multiple issues, like the ones mentioned above - in that case, it's important to make sure that you have fixed all of the errors in the sentence.

To fix these fragments, add a subject and make sure the verb is present in a correct form.

Dependent Clause Fragments

How to recognize these fragments: the sentence has a subject and correctly conjugated verb, but begins with a subordinating conjunction and isn't attached to another main clause.

The following words are common subordinating conjunctions. If the sentence begins with one of these, make sure it's attached to an independent clause. If not, it's a fragment!

Let's look at some examples of this errors:

One way to fix these fragments is to connect them to an independent clause.

You can also fix them by getting rid of the subordinating conjunction. This turns them into independent clauses that can stand on their own.

Added Detail Fragments

How to recognize these fragments: look for words like "such as," "including," and "for example" that start a sentence, but explain something in a previous sentence. If this kind of construction isn't attached to an independent clause with a subject and a verb, then it's a fragment.

In order to fix these fragments, add the detail fragment to the main sentence it is describing.

Finally, make sure that anything that comes before a colon can stand on its own as a sentence:

I know many different dances: the salsa, the polka, and the waltz.

Non-essential clause, appositive, or prepositional phrase fragments

How to recognize these fragments: cross out the non-essential clause, prepositional phrase, or appositive. Do you have a complete sentence left over? If not, you have a fragment.

How to fix these fragments: Add a subject or verb as needed. Make sure that if you eliminate the prepositional phrase or non-essential clause, that there is a complete sentence left.

What Is a Run-on?

A run-on is when two or more sentences run together and are not separated by the correct punctuation. There are three main types of run-ons:

• Comma splices
• Fused sentences
• Sentences joined by a conjunctive adverb and commas

Comma Splices

A comma splice is when two complete independent clauses (full sentences) have been joined together by a comma and nothing else. A comma can never join together two complete sentences on its own.

He had worked for the government for several years, he now wanted to try a job in a small start-up company.

How to recognize these run-ons: when you see a sentence with a comma in the middle, check to see if there is a coordinating conjunction (see this article for more info) that joins the sentences together, or if one of the clauses is a subordinate clause that begins with a subordinating conjunction. If not, the sentence is a run-on.

Fused sentences

A fused sentence is when two or more sentences run right into each other, with no punctuation at all.

He had worked for the government for several years he now wanted to try a job in a small start-up company.

How to recognize these run-ons: look to see if you have two unconnected subjects and verbs, with no indication of more than one independent clause (see above the correct ways to join two independent clauses).

Conjunctive adverb and a comma

The final type of run-on is a bit trickier. Conjunctive adverbs are used with periods or semicolons to connect two independent clauses, so if they're paired with two commas instead, it creates a run-on:

He had worked for the government for several years, however, now he wanted to try a job in a small start-up company.

However, conjunctive adverbs that are connecting two complete sentences punctuated with a period or semicolon are sometimes moved into a sentence. This is perfectly acceptable: 

He had worked for the government for several years. Now, however, he wanted to try a job in a small start-up company.

How to recognize these run-ons: when you see a conjunctive adverb (however, moreover, nevertheless, therefore, consequently, etc.) with commas on either side of it, make sure it's being used to transition from a previous sentence and not to connect two independent clauses.

To fix run-ons

...you will need to use the rules outlined in the first section to correctly join two sentences.

#1: Create two separate sentences.

He had worked for the government for several years. He now wanted to try a job in a small start-up company.

#2: Use a comma and a FANBOYS conjunction

He had worked for the government for several years, but he now wanted to try a job in a small start-up company.

#3: Use a semicolon

Remember that a semicolon is grammatically identical to a period - this concept is something the ACT tests a lot.

He had worked for the government for several years; he now wanted to try a job in a small start-up company.

#4: Use a semicolon and a conjunctive adverb

He had worked for the government for several years; however, he now wanted to try a job in a small start-up company.

#5: Make one of the clauses dependent

Although he had worked for the government for several years, he now wanted to try a job in a small start-up company.

#6: If the two clauses have the same subject, re-write as a sentence with one subject and two verbs.

Note that when you fix a sentence this way, you should not use a comma with your FANBOYS conjunction.

He had worked for the government for several years but now wanted to try a job in a small start-up company.

Specific Strategies for Fragment and Run-on Questions

As you're reading through the different passages on ACT English, if you come across a question that you think may be about fragments or run-ons, use the following steps:

Step 1

Carefully read the prompt if there is one. Sometimes the ACT will ask you to correct an error, and other times they will ask you to find the only answer that does NOT work.

Step 2

1. -ed or -ing verbs. Check for appropriate helping verbs.
2. Clause that begins with a subordinating conjunction. Check if it is connected to a main clause.
3. A separate sentence describing a previous sentence, with words like “for example.”
4. Conjunctive adverbs like “however” surrounded by commas
5. A semicolon followed by a FANBOYS conjunction
6. A single comma in the middle of the sentence - often a sign of comma splice

According to the ACT, not all mistakes are created equal. There are a few concepts they like to test more than others, and they have some obvious markers.

If the underlined section has a colon or semicolon, be on the lookout for a fragment on either side.

If the underlined section has a comma, it will very likely be a comma splice.

Immediately cross out any answer choices that make the above errors.

Step 3

If you are still uncertain about the correct answer: you can immediately eliminate anything that is grammatically identical. For example, a semicolon (;) is grammatically identical to a period and a new sentence. If one is incorrect, they will both be incorrect.

Step 4

Select a final answer choice that follows the above rules and also follows the standard style rules used on ACT English:

#1: No unnecessary prepositions or articles
#2: Pronouns must have clear antecedents
#3: Use fewer gerunds and participles if possible
#4: No dangling or misplaced modifiers
#5: No unnecessary commas
#6: Choose the most concise option that is also grammatically correct.

Let’s try one together…

Benjamin’s grandmother taught him to read, and he attended a one-room Quaker school when the farmwork slowed down during the winter.

From reading the prompt, I can see that the given sentence is correct as is, and so are three of the answer choices. This is a “backwards” question that asks us to find the only incorrect answer instead of the only correct one.

I can see that there is a comma in the underlined portion, so I need to see how it’s being used. It’s pretty obvious that the comma is being used together with the FANBOYS conjunction “and." This is one of the correct ways of joining two independent clauses, as detailed above.

From double checking I can see that I have two independent clauses with their own subjects and verbs: “Benjamin’s grandmother taught him to read” and “he attended a one-room Quaker school when the farmwork slowed down during the winter.”

So which of the answer options also show correct ways to join two independent clauses?

(A) has the independent clauses joined by a semicolon on its own. This is a correct way to join two independent clauses, so (A) is not the answer.

(B) joins the two independent clauses together in the same way that the original sentence does, with a comma and a FANBOYS conjunction. The only thing that is different is that it adds an extra adverb, “also," which is unnecessary but not incorrect.

(C) does not do anything to join the two clauses together - this is a classic example of a “fused” run-on sentence. Therefore, (C) is the correct answer as it is the only option that does not join the clauses together correctly.

But what if you aren’t sure? Just to check…

(D) separates the two independent clauses with a period, which is another correct way of dividing two independent clauses, so (D) is not the answer.

Now time to try some on your own!

Practice ACT Questions 

1. Joe realized the extent of the problem when his manager, Diane Watson, who had collated the material from the committee members present at the conference, began muttering, "It's all over now," this made him worry.

1. NO CHANGE
2. now" that
3. now." This
4. now,"

1. NO CHANGE
2. perforated, by being able
3. perforated, which is able
4. perforated, is able

1. NO CHANGE
2. dance in which it is performed
3. dance, performing
4. dance, performed

4. Around this time, the Glagolitic alphabet introduced by St. Cyril; became further integrated into the culture.

1. NO CHANGE
2. St. Cyril
3. St. Cyril:
4. St. Cyril,

5. To ensure the safety of the drug, the pharmaceutical company had it tested in several trials, however, they found no evidence of averse side effects.

1. NO CHANGE
2. which
3. who
4. he

6. Peter the Great, who founded St. Petersburg to be Russia's "window to the West" and indirectly named the city after himself.

1. NO CHANGE
2. West," indirectly naming
3. West," indirectly named
4. West" and

Answers: 1. C; 2. D; 3. D; 4. B; 5. B; 6. C

What’s Next?

Now that you’ve mastered one of the trickiest concepts on ACT English, time to check out some others! Read about how the ACT will test you on pronoun agreement, punctuation, and wordiness and redundancy.

Need to review some of the basics before moving forward? Brush up on the fundamentals of grammar with our parts of speech guide.

Want to make sure you have the right method of attack for this section? Read our guide about the best way to approach ACT English questions.

Aiming high? Read this article for top tips for a 36 on ACT English from a perfect scorer.