Commas are impressive little punctuation marks. They can do many things — separate words in a list, set off names, or appear after introductory clauses, to name a few. But one thing they can’t do is join together two complete sentences.
What Is a Comma Splice?
When a comma is used to join two independent clauses, it’s called a comma splice, and it’s a grammatical error. Commas can do a lot, but they’re not strong enough to combine two complete sentences alone. Take a look at these examples:
She spent the day baking, she didn’t clean up afterward.
Anita ate cookies, Colin drank tea.
His car got a flat tire, he arrived late.
Each of these sentences contains two independent clauses. In other words, on either side of the comma, there is a complete sentence with a subject and a verb. The topics are closely related, so it makes sense to join them together. There are several ways to do this, but using a comma alone is not one of them.
Use a Coordinating Conjunction
Two closely related sentences can be joined using coordinating conjunctions. Remember the seven coordinating conjunctions by using the acronym FANBOYS: For, And, Nor, But, Or, Yet, and So. Let’s rewrite the previous examples by inserting coordinating conjunctions:
She spent the day baking, yet she didn’t clean up afterward.
Anita ate cookies, and Colin drank tea.
He was already late, but he got a flat tire.
This tactic works well to show a contrast or the cause and effect between the two closely related ideas. The clauses have a logical relationship with each other.
Use a Semicolon
If there’s no apparent conjunction to join the two sentences, try replacing the comma with a semicolon. Unlike a comma, a semicolon is strong enough to join two complete sentences. It’s important to note, however, that a coordinating conjunction should not be used if a semicolon is used.
She spent the day baking; she didn’t clean up afterward.
Anita ate cookies; Colin drank tea.
He was already late; he got a flat tire.
This works best when it’s unclear what conjunction would join the two sentences, or when the ideas presented appear in a time-based sequence.
Use a Period
Another way to fix a comma splice is to break up the sentences with a simple period:
She spent the day baking. She didn’t clean up afterward.
Anita ate cookies. Colin drank tea.
He was already late. He got a flat tire.
While grammatically correct, using a period does change the flow of the writing. It will give the sentences a shorter, staccato feel, so consider the intent of the words when determining which approach is best.
Use a Subordinating Conjunction
Finally, complete clauses can be joined by a subordinating conjunction when there is an independent clause and a dependent clause. Common subordinating conjunctions include “because,” “while,” “unless,” “whenever,” “however,” “though,” “when,” and “so.”
She spent the day baking though she didn’t clean up afterward.
Anita ate cookies while Colin drank tea.
Before he got a flat tire, he was already late.
These conjunctions show a cause-and-effect relationship or a shift in time between two sentences. Generally, a comma is not required in front of a subordinating conjunction, however, a comma is used in the sentence when the dependent clause comes first. As in the case of the flat tire, the dependent clause, with the subordinating conjunction “before,” is at the front of the sentence. This punctuation is counter to coordinating conjunctions, which require a comma to join the two sentences.
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