What Is a Comma Splice? Definition and Ways to Avoid It

Comma Splice (Run-on Sentence)

A comma splice, also known as a type of run-on sentence, is a common grammatical error in English. It occurs when two independent clauses are joined with only a comma.

A comma alone is not enough to connect two complete sentences properly. To join two independent clauses in a grammatical way, you need a coordinating (FANBOYS) conjunction, a semicolon, or another appropriate structure.

TOEFL Preps

Independent vs. Dependent Clauses: A Clear Explanation

🕒️February 22, 2026

As you improve your English and deepen your grammatical knowledge, one important threshold is whether you fully understand the concept of a “clause,” including the distinction between independent and dependent clauses.Understanding what makes a clause, and how independent clauses differ from dependent clauses, is essential for consistently producing advanced grammatical sentences.A solid understanding of clause structure is key to using advanced English, not only for TOEFL but also for academ...

Look at the following example:

× I have a dog, it is cute.

This sentence is ungrammatical because the two independent clauses are joined with only a comma.

• First independent clause: I have a dog
• Second independent clause: it is cute.

Because both clauses can stand on their own, each of them is an independent clause. Therefore, you need something more than just a comma to connect them properly.

I have a dog, and it is cute.

I have a dog; it is cute.

In these examples, the two independent clauses are connected appropriately. In the second sentence, a semicolon is used to link the two clauses.

Be Careful: A Comma Splice Is Always Wrong

A comma splice always creates an ungrammatical sentence. In standard English, two independent clauses cannot be joined correctly with only a comma.

For that reason, you should be especially careful to avoid comma splices in TOEFL writing, other academic tests, and formal writing in general.

More over, a comma splice doesn’t just create a grammatical error; in fact, in some cases, it can also make the relationship between two clauses unclear and weaken the meaning of the sentence.

Look at the following example:

× I can’t go to school, I need to do something important.

In this sentence, two independent clauses are connected with only a comma. As a result, the relationship between them is not expressed clearly. Does the second clause give the reason the speaker cannot go to school? Or is it meant to express contrast, as in “I can’t go to school, but I need to do something important”?

This is one reason comma splices are problematic. They do not only create grammatical errors, but can also blur the logical relationship between ideas.

Ways to Avoid Comma Splice Error

To avoid comma splices, you need to understand the structures that can connect ideas more appropriately. There are several common ways to fix or avoid this error.

• Using a coordinating conjunction
• Using a semicolon
• Using a colon

Now, let’s look at how each of these approaches can help you avoid a comma splice.

Using a Coordinating Conjunction (FANBOYS)

One of the most straightforward ways to avoid a comma splice is to connect two independent clauses with a coordinating conjunction. The seven coordinating conjunctions are often remembered by the acronym FANBOYS: for, and, nor, but, or, yet, and so.

When a coordinating conjunction joins two independent clauses, a comma is usually placed before the conjunction. Look at the following example:

TOEFL is a useful test for measuring English proficiency, but it requires a solid understanding of English to achieve a high score.

In this sentence, the two independent clauses are joined by the coordinating conjunction but. Because the clauses are connected properly, the sentence is grammatical.

What About Conjunctions Other Than FANBOYS?

Not all conjunctions work in the same way. Conjunctions such as “because,” “while,” and “although” are called subordinating conjunctions. Unlike coordinating conjunctions (FANBOYS), subordinating conjunctions introduce a dependent clause, which can’t stand alone as a complete sentence.

For example, consider the conjunction “although” used in a sentence.

Although many people visit Las Vegas in the hope of becoming rich, only a small number actually make a fortune.

This sentence consists of two parts:

• Dependent clause: Although many people visit Las Vegas in the hope of becoming rich
• Independent clause: Only a small number actually make a fortune.

The first clause is dependent, which means that it can’t function as a complete sentence by itself. If you stop at “Although many people visit Las Vegas in the hope of becoming rich,” the sentence feels incomplete because the listener expects additional information.

This is an important difference between coordinating and subordinating conjunctions. A coordinating conjunction joins two independent clauses. A subordinating conjunction, by contrast, introduces a dependent clause and connects it to an independent clause.

Using a Semicolon

A semicolon can be used to join two related independent clauses. It is often used when the relationship between the two clauses is already clear, especially when the second clause adds a contrast or a reason.

TOEFL Preps

Two Effective Punctuation Marks in TOEFL Writing: Colon and Semicolon

🕒️January 31, 2026

How to Ace TOEFL Writing?TOEFL is an English proficiency test, so its primary purpose is to evaluate a test taker’s language skills. Writing, of course, is no exception.This means that your writing performance is evaluated largely based on the quality of your language rather than the originality of your ideas. In other words, unique or highly creative content itself plays a limited role in scoring.This stands in clear contrast to school writing, where original ideas are often valued more high...

Consider the following sentence:

I feel sick today; I have to go to school and take the mid-term exam.

In this sentence, the relationship between the two clauses is clear. The second clause contrasts with the first one: even though the speaker feels sick, the speaker still has to go to school because of the exam.

In cases like this, a semicolon can be used effectively to connect two independent clauses without a coordinating conjunction.

Using a Semicolon with a Conjunctive Adverb

In addition to its basic use, a semicolon is often used with an adverb and a comma in the following pattern:

• independent clause + ; adverb, + independent clause

This structure allows you to connect two independent clauses clearly and smoothly. Take a look at the following example:

I like dogs; however, I am allergic to dog hairs.

This sentence consists of two parts:

• First independent clause: I like dogs
• Second independent clause: I am allergic to dog hairs.

To connect two independent clauses correctly, you need an appropriate structure. In this sentence, the combination of a semicolon, the conjunctive adverb however, and a comma links the two clauses properly.

This pattern is common in formal writing. In the example above, however shows contrast, so the expression works in a way similar to the coordinating conjunction but.

Note that the semicolon is essential here. If you replace it with a comma, the sentence becomes ungrammatical because a comma alone cannot correctly join two independent clauses.

Here’s another example:

The roads were covered with ice; therefore, many drivers decided to stay home.

In this sentence, “therefore” is an adverb. The semicolon before it and the comma after it help connect the two independent clauses correctly.

This structure is useful when you want to show a clear logical relationship between two complete clauses in formal writing. In this example, the second clause shows a result of the situation described in the first clause.

Using a Colon

Another way to connect two independent clauses is to use a colon. However, a colon can be used only when the second clause explains, develops, or gives specific details about the first clause. If that relationship is missing, a colon is not appropriate.

Take a look at the following example:

My dog is smart: he can count numbers up to 10.

This sentence consists of two independent clauses. A colon is used here because the second clause gives specific information that supports the idea expressed in the first clause. In other words, the second clause explains why the speaker says that the dog is smart.

This is the key point when using a colon between two independent clauses. The second clause must develop or explain the meaning of the first one.

Here is another example:

She had one clear goal: she wanted to study abroad.

In this sentence, the clause after the colon explains the content of the first clause more specifically. The first clause introduces a general idea, and the second clause gives the exact detail of that idea.

This is a typical use of a colon. A colon can connect two independent clauses when the second clause develops or explains the meaning of the first one.