How to fix a comma splice

How to fix a comma splice

The comma splice is a very common punctuation error. In this post, I’ll describe comma splices and outline how to identify, avoid, and repair them.

Run-on sentences and comma splices

Before I dive into a discussion about comma splices, I should say a few words about run-on sentences. There’s a pervasive myth that run-on sentences are simply long, unwieldy sentences. They’re not. Rather, a run-on is a specific grammatical mistake. It occurs when two independent clauses (i.e., stand-alone sentences complete with a subject and a verb) are joined without any punctuation or conjunction:

Traffic is terrible I’m going to be late for work.

The two independent clauses in this example are “Traffic is terrible” and “I’m going to be late for work.” No punctuation or conjunction separates them, so the sentence is a run-on.

A comma splice is similar to a run-on sentence in that it also occurs when two independent clauses are improperly connected. Unlike a run-on sentence, which is formed when two independent clauses are connected with no punctuation or conjunction, a comma splice is formed when the clauses are joined by nothing but a comma:

Traffic is terrible, I’m going to be late for work.

Independent clauses need to be joined by one of the following: a period, a semicolon, or a coordinating conjunction. Commas can only join independent clauses with the help of a coordinating conjunction. If there’s a comma and no coordinating conjunction, the sentence contains a comma splice.

Writers tend to form comma splices because they want to show a close connection between two ideas. In my example, being late for work is the result of terrible traffic. To many authors, a period suggests a change in topic. A comma, on the other hand, doesn’t seem to draw such a distinction.

Common comma splices

A comma splice can form in any type of sentence, but I’ve noticed a few instances that seem to produce a disproportionate number of them. First, the adverbs however, thus, and therefore seem to trip writers up:

Traffic is terrible, thus, I’m going to be late for work.

The two independent clauses in this sentence are “Traffic is terrible” and “Thus, I’m going to be late for work.” Again, writers often create comma splices with these adverbs because they are attempting to draw a close connection between the two clauses.

Second, writers often mistakenly use then as a conjunction:

Mark laid the hardwood floor, then he installed the baseboards.

The two independent clauses in this case are “Mark laid the hardwood floor” and “Then he installed the baseboards.” Then isn’t a conjunction, so it can’t join independent clauses.

Third, short, conversational independent clauses at the beginning of a sentence often produce comma splices:

I don’t know, hiking isn’t that fun.

Let’s be honest, baseball is the best sport.

“I don’t know” and “Let’s be honest” can both stand alone as their own sentences, so they are independent clauses. Joining them to another independent clause with nothing but a comma therefore produces a comma splice.

Fixing comma splices

As I noted above, periods, semicolons, and coordinating conjunctions can join independent clauses, so there are three ways of fixing a comma splice.

1. Replace the comma with a period: 

The easiest way to fix a comma splice is to replace the comma with a period. Recall my earlier example of a comma splice (“Traffic is terrible, I’m going to be late for work”). Removing the comma and using a period corrects the mistake:

Traffic is terrible. I’m going to be late for work.

The problem with a period is that it suggests the second independent clause is a new idea and is unrelated to the first independent clause. Que the the semicolon.

2. Replace the comma with a semicolon

If you think a period does a poor job of connecting the ideas in two independent clauses, replace the comma with a semicolon instead. Semicolons imply a closer link between two sentences:

Traffic is terrible; I’m going to be late for work.

Use the semicolon sparingly, however; they lose much of their effect if they appear too often in the text. If you want to create the same sense of connection between two clauses without using the semicolon, consider using a coordinating conjunction instead.

3. Add a coordinating conjunction

One of the principal functions of a coordinating conjunction is joining independent clauses. But, and, and so are probably the most common:

Traffic is terrible, so I’m going to be late for work.

As I discussed in Chapter 1, we almost always keep the comma when joining independent clauses with a coordinating conjunction.


Comma splices are a common punctuation mistake, and even experienced writers create them. Comma splices even get past some editors and into published books. The key to preventing them is being able to identify independent clauses. If you can spot subjects and verbs, you can spot independent clauses. Then it’s simply a matter of joining your independent clauses with a period, semicolon, or coordinating conjunction.

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