Can you please tell me: when is it advisable to use a comma before the word "because" when stating the reason of something? Since I've already seen contexts with and without a comma before because, and it's so confusing to me.
Hello, Jessy—Generally speaking, we do not use a comma before a "because"-clause when the "because"-clause is the focus of the sentence, i.e., when the main point of the sentence is to give an answer to the question "Why?"
- John was absent yesterday because he was sick.
- John was hired because he was the most qualified candidate.
Often, in the contexts in which such sentences are uttered or written, the information conveyed by the main clause (that John was absent yesterday, that he was hired) is already known; the "because"-clause gives new information.
When a "because"-clause is set off by a comma, the information presented in the "because"-clause is treated as being of separate, subordinate, or equal importance with respect to the information conveyed in the main clause.
- John will be calling in an hour, because he has a question.
- John likes that restaurant the most, because it has the best wine.
When the main clause is negative, a comma (or the lack thereof) before the main clause carries a special significance, though not everybody is aware of it. It is an advanced comma rule. Consider the following sentences:
- Mary wasn't hired because she has a degree in marketing.
- Mary wasn't hired, because she has a degree in marketing.
Technically, the sentence without the comma expresses that she did get hired, but the reason was not that she had a degree in marketing; she was hired for some other reason. "Not" effectively negates the "because"-clause.
Technically, the sentence with the comma expresses that she did not get hired, and the reason she didn't is that she has a degree in marketing. The interviewers were looking for someone with a different sort of degree.