Before I start explaining what a comma splice is and how to correct one, I want to make it clear that not all comma splices are errors.* Unfortunately, few American English teachers are aware that there is a type of comma splice that is perfectly acceptable, and so they mark all comma splices as errors.
If you have read some of my other articles on grammar and usage, you know that there are certain "rules" that need not be slavishly obeyed. I don't recommend gratuitously splitting an infinitive or ending a sentence with a preposition, simply because so many people are likely to jump on you when you do. However, when the occasion clearly calls for either a split infinitive or a preposition at the end of the sentence, I say go for it. But even when a properly handled comma splice would produce just the rhetorical effect I am after, I won't use it.
No doubt you are disappointed in me. The fact is, though, that in the U.S. a lot of people who are sure they understand the "rules" of English firmly believe that all comma splices are not just errors, but really big errors, and that any one who commits a comma splice is demonstrating a fundamental inability to control a sentence. If I were to use a perfectly acceptable comma splice, I can be sure that an awful lot of people would assume that I have no mastery of sentence boundaries. They would be wrong, but I would never get the chance to argue the point, so their judgment would stand.
Sometimes it seems that the rule against comma splices is the only rule that many people--English teachers especially!--have managed to master, and so they are always on the hunt for an opportunity to wield it against someone. While it is true that in American usage most comma splices are errors, it is also true that some are worse errors than others, and some are not errors at all.
I am not even sure it is considered a matter of concern in British usage, and if any of my readers are from the U.K., I would like to know whether current usage there abhors the comma splice as does American usage.
Now to business.
WHAT IS A COMMA SPLICE?
Quite simply, a comma splice is the attempt to join two independent clauses with a comma, but without a coordinator.
Let's back up for a moment. First of all, according to the definition most of you learned in grade school, an independent clause is one that can stand alone as a sentence. (This is not the most precise or useful way to define an independent clause, but it will do for now.) When two independent clauses are next to each other, you have only two choices: you can either join them, or you can separate them.
(1) To join two independent clauses, you must use a coordinator. The coordinators are the correlatives and the coordinating conjunctions. (Correlatives don't figure into comma splices, so we will not worry about them.) The coordinating conjunctions are and, but, or, nor, yet, and so. You can remember them by combining their first letters into the pseudoword "anboys." Your English teachers and your usage handbooks also listed "for" as a coordinating conjunction. Forget that. As a conjunction "for" translates as "because," and serves as a subordinating conjunction, just as "because" does.
(2) To separate two independent clauses, you must use some form of end-stop punctuation. Here are all of your possible choices: the period [.], the exclamation point [!], the question mark [?], and the semicolon [;]. (Remember, a semicolon is a weak period, not a strong comma. The semicolon fragment is a common error, one I deal with in "Colons, and Semicolons, and Bears!")
What this means is that if you have two independent clauses with nothing between them but a comma, you have failed either to join them with a coordinator or to separate them with end-stop punctuation. (You will notice that the comma is not on either of those two lists.) Thus, you have a comma splice, which is a form of run-on sentence.
Here is an example of a comma splice, followed by several different ways of correcting it:
COMMA SPLICE: I got up late this morning, I didn't have time for breakfast.
I got up late this morning. I didn't have time for breakfast.
I got up late this morning; I didn't have time for breakfast.
I got up late this morning, so I didn't have time for breakfast.
I got up late this morning, and I didn't have time for breakfast.
Notice that in the latter two corrections, the coordinating conjunction joining the two independent clauses is preceded (not followed) by a comma. (That's about a 90-95% rule. See"Commas with Compound Sentences"for information about when that comma can be omitted.) What causes a comma splice is not the comma between the two clauses, but rather the absence of the coordinator in the attempt to join the clauses.
A DIFFERENT STRATEGY: If you choose to turn one of the clauses into a subordinate (dependent) clause, then you can use just the comma between the two clauses:
Because I got up late this morning, I didn't have time for breakfast.