This question already has an answer here:

Suppose I am talking about three people:

John, Jane "," or Joey could finish the task on time.

Do I need the comma before "or"?

EDIT: This asks about using a comma with "or", not "and". So this question is different from Is it necessary to use commas in lists before the conjunction?.

marked as duplicate by Catija, ColleenV, Nathan Tuggy, Brian Tompsett - 汤莱恩, shin Jul 16 '16 at 6:09

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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    The rules are identical... and your question was originally about both "and" and "or". – Catija Jul 15 '16 at 17:04

You have asked one of the most hotly debated questions in English usage! That comma is called the serial comma or Oxford comma. (Here is a discussion about it on english.stackexchange.com.) Some people say you would use it; others say you should not. The problem is that either way can make a sentence less clear.

With no comma:

I would like to thank my parents, Ayn Rand and God.

That makes it look like my parents are Ayn Rand and God.

With the comma:

Those at the ceremony were the commodore, the fleet captain, the donor of the cup, Mr. Smith, and Mr. Jones.

That makes it look like the donor of the cup was Mr. Smith.

And sometimes it's unclear either way:

The highlights of his global tour include encounters with Nelson Mandela, an 800-year-old demigod and a dildo collector.
The highlights of his global tour include encounters with Nelson Mandela, an 800-year-old demigod, and a dildo collector.

The first version, without the comma, makes it look like Nelson Mandela is an 800-year-old demigod and a dildo collector. The second version, with the comma, still makes it look like Nelson Mandela might be an 800-year-old demigod (but not a dildo collector).

In your example sentence it doesn't really make any difference: nobody is going to be confused either way. My personal opinion is that it looks and reads better with the comma.

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    Without comma, one could read ‘John’ as vocative. With comma, one could read ‘Jane’ as vocative. – Anton Sherwood Jul 15 '16 at 21:25
  • @AntonSherwood - Good point, I hadn't thought of that. It seems like an unlikely place for a vocative, but the potential is definitely there. – stangdon Jul 15 '16 at 21:29
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    It's admittedly strained; so are most examples presented in such arguments. Ambiguity can generally be sidestepped by changing the sequence of items. – Anton Sherwood Jul 15 '16 at 21:35

This is known as the Oxford or Serial comma, and whether or not writers use it is completely a matter of style. Personally, I prefer using it, as it helps differentiate each item in the list. But it's not necessary.

  • Sometimes people say things like "I hate the oxford comma" which doesn't make sense to me. If they really understood what it does, they would know that it removes ambiguity. – max pleaner Jul 15 '16 at 23:13
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    It is not "completely" a matter of style. There are cases where the Oxford comma is useful for clarity, and times when it makes sentences less clear. Of course, there are also many situations where it doesn't matter at all. No one should always leave it off or always include it. Read the sentence you're writing aloud and pause on each comma. If it sounds right, you're good. If it sounds wrong, add or remove the comma. – ell Jul 15 '16 at 23:45