Before I begin, let me say this: There are no unbreakable writing rules. Practiced, nimble writers stick to what we call rules until those rules don’t serve them, and then they abandon the rules for a sentence or two or three. Still, you do want to know what a reader expects, right?
Okay. I'm about to tackle the comma splice. This, comma splicing, is something writers of all ages and abilities do, and when it’s not intentional and purposeful, it makes a reader’s job more difficult. That’s the kind of stuff we all, as writers, want to avoid most of the time. (And if you've read my book, you know that comma splices grate on my very soul.)
So: A comma splice happens when you have two independent clauses, which are clauses that could be sentences all on their own, smashed into the same sentence and separated by a comma only.
LeBron won his first championship, he earned many critics’ respect.
See the comma splice? “LeBron won his first championship” could stand on its own as a sentence, right? So could “He earned many critics’ respect.” That means a comma can’t be the only thing between these two clauses.
Watch this clip from Star Wars as illustration of my point: Star Wars Comma Splice!. In the clip, you’ll see two walls closing in on our heroes. Think of these walls as independent clauses. Our heroes try to keep them apart with a comma (a strange metal bar thing they find in the compactor with them), but the comma isn’t strong enough, on its own, to keep the walls/independent clauses apart.
It’s just not what a comma does. A comma’s great at separating stuff in a list (e.g., “Now LeBron has won three MVP awards, an Olympic gold medal, and an NBA Championship”). It can also help us get from a dependent part of a sentence to the independent part that can stand on its own.
When LeBron won his first championship, he earned many critics’ respect.
See the word When? That tells the reader that there needs to be more to the sentence than just the first clause, which means the first clause (i.e., “When LeBron won his first championship”) is dependent. It depends on another clause. In this case, then, the comma works perfectly, sitting between the dependent part of the sentence and the independent part. Of course, if you flip this sentence around, you really don’t need a comma at all:
LeBron earned many critics’ respect when he won his first championship.
Why not? Well, it has a lot to do with the feel and momentum of the sentence. In this case, you’ve already articulated the main, independent part of the sentence and it doesn’t feel right (does it?) to stop before getting to the clause that enhances that point. In “When LeBron won his first championship, he earned many critics’ respect,” the comma feels necessary because the reader has to wade through the dependent part of the sentence before arriving at the independent part. That’s how this makes sense to me, anyway.
You could write it this way, as well:
LeBron won his first championship, earning many critics’ support.
In this case you’ve removed the subject “he” from the second part of the sentence and changed the verb to an –ing form. That means the second part is now a phrase instead of a clause (a clause needs some kind of action, which is called a predicate, and a subject to perform that action).
You have (at least) three other options, if you’d like to keep the same words you began with.
First, you could use a period:
LeBron won his first championship. He earned many critics’ respect.
Second, you could use a comma and a conjunction (For, And, Nor, But, Or, Yet, So):
Lebron won his first championship, and he earned many critics’ respect.
Third, you could use a semicolon:
LeBron won his first championship; he earned many critics’ respect.
Which version do you like best? Of these three, I might choose the third option because it doesn’t feel as compartmentalized as the first and removes the word “and,” which doesn’t feel right to me here because it suggests a chronology (first this happened, and then this happened) that I don’t believe exists, given that LeBron earned his critics’ respect while winning his first NBA championship. Of course it depends on the form of the piece and on my audience, too. If I was asked to give a short play-by-play summary, I’d go with the period. If these thoughts fit into a longer piece, I’d go with the semicolon. It’s all about feel. The best part? You don’t need to agree with me. You get to make these decisions for yourself every time you sit down to write.
If you rewatch the Star Wars clip, you’ll notice that C-3PO and R2-D2 (the robots) are hustling about the control room trying to get their friends and that pathetic metal bar/comma in the trash compactor some help. When R2 shuts the power down in the compactor, he grammatically gives the bar/comma either a conjunction like “and” or dot on top to make it a sturdier mark of punctuation—a semicolon. Or maybe he disregards the bar/comma and replaces it with a period.
The moral? Don’t let scrawny commas splice your sentences! Commas serve many noble purposes; just don’t allow them to make your reader’s job more difficult.