Q. My question relates to the proper use of the comma when using a subordinate clause introduced by the pronoun “which” or “who.” My impression is that a comma to set off the clause is proper sometimes but not always. For example, if I say, “I have a car which has four doors,” a comma introducing the clause is not appropriate. However, if I say, “My car, which has four doors, is blue,” the comma is proper. I am not quite sure how to articulate the rule for when the comma is proper and when not. Can you help me?

Q. In the sentence “Researchers at the University of California, Riverside and the University of Southern California determined . . . ,” should there be a comma after “San Diego”?

Q. Do I need to put a comma here: fresh, local produce?

Q. I have a question about using a comma with the word and. I am an editorial intern for an art journal, and the most recent piece I am editing has a sentence written thus: “Henry Darger is both illuminating and, at times, frustrating.” The question we have been debating in the office for a significant amount of time today is whether or not there should be a comma inserted after the word illuminating to offset the and.

Q. I work for a company that says they’re focused on building client relationships. However, they insist when we address an email to one of our own clients whom we know well that we put a comma in hi, hello, or good morning, Joe. I have been told that this is a very formal way of addressing someone. Help!

Q. In the following sentence, is a comma required (or even recommended) before “and her ten-year-old son”? “She is especially distraught when her preteen daughter, Pam, rebels by befriending a navel-pierced neighbor and her ten-year-old son, Joe, betrays her by making contact with the father.” I see this clause as being introduced by the same when that introduced the clause before it, and I would opt for no comma. Since the sentence is long, would it be acceptable to repeat the word when before the other clause? (“She is especially distraught when her preteen daughter, Pam, rebels by befriending a navel-pierced neighbor and when her ten-year-old son, Joe, betrays her by making contact with the father.”)

Q. All of this plus installation, at no cost to you. Is the comma necessary here? I think it is added sometimes to denote “and,” but then maybe an em dash would achieve greater dramatic pause or surprise.

Q. Hi, Chicago—I’m replying to your e-mail answer more than seven years later because I’m still trying to wrap my head around punctuating sentences like these:

She was still so shocked, it took her a while to find her voice.

He was so fixated on his game, he had no idea I’d entered the room.

Do they require the comma? Based on your seven-year-old e-mail reply (“I don’t know of any such rule”), I’ve been deleting most such commas. Occasionally, I’ll replace the comma with a semicolon. But I guess what I’d like to know now is this: Is there any rule (preferably somewhere I can cite) that governs this type of sentence?

Q. Does the following sentence require a comma after says? The person who says “I no longer get anything out of reading” has stopped running up against questions to think about as he or she reads.

Q. Hi, I have a simple comma question. Here’s the sentence:

Readers will understand that he is subject to the expectation that he must be the sole financial provider for his family, and that he is hesitant to get married because he is unemployed and without prospects.

I think the comma is unnecessary, since “that he is hesitant to get married because he is unemployed and without prospects” is not really an independent clause. Plus, it seems clear and readable enough without it. But it was pointed out to me that “he is hesitant to get married because he is unemployed and without prospects” is an independent clause, so there should be a comma. What do you say?