The Remedy of the Week: Comma splices

Each week proofreader Hannah Jones discusses and offers a remedy to common problems we encounter when writing. Today she explains what comma splices are and how to avoid creating them.

What is a comma splice?

A comma splice (sometimes referred to as a run-on sentence) occurs when a comma is incorrectly used to link two independent clauses.

Unsure of what exactly constitutes an independent clause? Let's have a quick recap. An independent clause is one which can stand by itself as a sentence and expresses a complete thought.

Consider the following sentence:

After going to school, Mary did her homework.

'Mary did her homework' is an independent clause; it can stand alone:

Mary did her homework.

However, 'After going to school' is a subordinate clause; it does not express a full thought and cannot form a sentence by itself:

*After going to school.

A comma can link an independent clause to a subordinate clause (as in 'After going to school, Mary did her homework.'), but it is not strong enough to link two independent clauses:

*Mary is a good student, she always does her homework.

Here the comma is 'splicing' two clauses that were already complete on their own.


As always, there are certain exceptions to this 'rule'. Perhaps the most famous is: I came, I saw, I conquered. Some style guides suggest that usage such as this – when the clauses are short and very similar to each other in form – is acceptable. However, if you are writing anything formal, it is best to avoid comma splices; they can make your writing look unprofessional or careless.

How to avoid a comma splice

Use a full stop

This separates the independent clauses into two complete sentences:

Mary is a good student. She always does her homework.

This is particularly useful if the two independent clauses are quite long.

Mary enjoys reading a great variety of different books. The last three books she read were a psychological thriller, a historical romance and an autobiography.

This method does, however, somewhat weaken the link between the two clauses.

Use a semicolon 

If the two independent clauses are closely related, it may be preferable to use a semicolon.

Mary is a good student; she always does her homework.

This is an elegant solution and retains the link between the two clauses. For further discussion on the uses of the semicolon, see my recent blog post.

Use a conjunction 

In some contexts, it may be appropriate to use a conjunction to link the two independent clauses. 

Mary loves to read and she is also very sporty.

John likes playing tennis, but Mary prefers football.

With conjunctions such as 'but', 'so' and 'because', a more complicated relationship between the two clauses can be expressed.

Hannah Jones is a professional freelance proofreader and owner of The Remedy of Errors.

Visit her website at The Remedy of Errors. She can also be found on Twitter @remedyoferrorsFacebook and LinkedIn.