Contrary to what grammar-checkers sometimes believe, a comma usually precedes ‘because” as a trailing clause. The trailer is separate from the truck. Sometimes, the comma doesn’t matter much. But at other times, the lack of a comma makes the statement opposite from what the author intended.
The determining factor is whether the ‘because” clause is explanatory (with the comma) or restrictive (without the comma). This is especially crucial when the “because” clause follows a negative statement.
Example:
Explanatory: Johnny didn’t leave the house, because he wanted to play with his train set. (He would have left the house, but the love for his train set kept him inside.)
Restrictive: Johnny didn’t leave the house because he wanted to play with his train set. (He didn’t care about his train set. He stayed inside for some other reason.)
Since no result can precede its cause, it’s often best to put the “because” clause at the beginning of the sentence, where it becomes an introductory clause followed by a comma. The exception to that guideline is times when the clause is restrictive. In those rare cases, it works best at the end, without the comma.
Explanatory: Because he wanted to play with his train set, Johnny didn’t leave the house. (Now the meaning is certain. Why? We’ve set the cause in the reader’s mind before the action.
In the restrictive form, the clause doesn’t work at the beginning. That’s because the cause is something else.
Confused yet? At least a dozen times, I’ve gone through this issue with an English teacher. Each time, I explain it, and she understands. And then I have to explain it again. That’s fine. I don’t mind repeating myself.
In deep point of view, we often want to avoid “because” clauses, because they are a “tell,” explaining, not showing.
Consider this example: He worships and praises God because he is a righteous angel.
Should we have a comma before “because”? This sentence can confuse readers because the antecedent for the second pronoun “he” isn’t clear. (I just used “because” in the restrictive sense, with no comma.) Readers can’t be sure the first “he” in the sentence is the same person as the second “he.” Without the comma, they are inclined to incorrectly connect the clause with “God.” Yet the existence of the comma doesn’t eliminate the chance of a misread.
Better: Because he is a righteous angel, he worships and praises God. (Now we have the two “he” words together, and the meaning is clear.)
A similar example:
Restrictive: He worships in church because he’s a righteous angel. (Being a righteous angel, he wouldn’t think of worshiping anywhere else.)
Explanatory: He worships in church, because he’s a righteous angel. (Because he’s a righteous angel, he would never go to church just for entertainment. He goes there to worship. The antecedent is clear with a trailing “because” clause, but I like the clause better at the beginning of the sentence, don’t you?) Because he’s a righteous angel, he worships in church.
Now lets look at this example:
Explanatory: She honors the woman, because she is her teacher. (The woman is her teacher, so she wants to honor her. The parallel structure makes “teacher” clearly be the woman, so the meaning of “she” is clear. We can’t put the clause at the beginning without changing the meaning.)
Different meaning: Because she is her teacher, she honors the woman. (“She” is the teacher, and the woman is “her.”)
Restrictive: She honors the woman because she is her teacher. (In the restrictive sense, we have the subtle distinction of necessity. She would always want to honor a teacher.)
If you’re not totally confused by now, you’re in the brilliant category.
This concept is highly technical and difficult for most writers to grasp, even English teachers. So my general guideline is to say, “Always put a comma before because. Leave out the comma only when it seems absolutely not right. That said, see if the clause will work better at the beginning of the sentence, an introductory phrase followed by a comma.”
