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Should I put a comma before the last item in a list?
Until relatively recent times, I always concluded a series in this manner, eg.: "while walking through the park yesterday, I saw dogs, pigs, kangaroos, mountain lions, zebras and wolves.
Eventually, it occurred to me that, for clarity's sake, that is to indicate that the last two items mentioned are not related as a pair, I should end such a sentence as "...mountain lions, zebras, and wolves." I read that this use of the comma is called an "Oxford" commma.
I think that the former use has just an aesthetic appeal, whereas the latter use has a more practical, clarifying function. I'm inclined, these days, to use the latter style.
Is this indeed the "Oxford" comma, and, if so, is it considered correct, incorrect, or just a matter of preference?
Thanks,
-Gavin