The word because causes a lot of problems with commas. It’s a confusing word used with a confusing punctuation mark. Here’s what happens.
A writer joins two independent clauses with because, which is a conjunction, and puts a comma in front of it. This is wrong.
Incorrect Example: I was sure the day would be nice, because the night was stormy.
Well, we already know Zen Comma Rule D: Put a comma before a coordinating conjunction that joins two independent clauses. The example, using because, seems to fit this rule. Right? After all, we seem to have two independent clauses joined by because, which is a conjunction: (1) I was sure the day would be nice and (2) the night was stormy.
Here’s the problem. Because is NOT a coordinating conjunction, so the rule doesn’t apply. Because is a subordinating conjunction, which means it starts a dependent clause. In this sample, we have an independent clause joined to a dependent clause, not two independent clauses.
Also, because is an essential part of the meaning of the sentence. Without that word, we would have two unrelated ideas. Because tells us that the second part causes the first part.
Put all this together, and we know not to put a comma before because. Now we know Zen Comma Rule F: Don’t use a comma before because when joining two clauses–unless needed by another rule.