After a lifetime of being wishy-washy about the serial comma, I’ve reached a decision: I’m going to use it all the time.
Such a momentous decision is, of course, a deeply personal matter. The pros and cons are widely, frequently, and hotly debated.
Here is some information that may enable you to make the decision for yourself, if you haven’t already done so.
serial comma: (also Oxford comma) n. a comma used after the penultimate item in a list of three or more items, before ‘and’ or ‘or’ (e.g. an Italian painter, sculptor, and architect). –Penguin Writer’s Manual.
Oxford comma: n. [after the preferred use of such a comma to avoid ambiguity in the house style of Oxford University Press] a comma immediately preceding the conjunction in a list of items. –OED
Some writers call the Oxford comma the “Harvard comma.”
Here’s a sentence with a serial comma: The Three Stooges are Larry, Moe, and Curly.
Here it is without a serial comma: The Three Stooges are Larry, Moe and Curly.
PRO serial comma
The Chicago Manual of Style (2009)
When a conjunction joins the last two elements in a series, a comma—known as the serial or series comma or the Oxford comma—should appear before the conjunction. Chicago strongly recommends this widely practiced usage, blessed by Fowler and other authorities… 6.19
The Elements of Style (2000)
In a series of three or more terms with a single conjunction, use a comma after each term except the last.
The stated rule seems ambiguous to me, but the examples that follow it are clear:
red, white, and blue
gold, silver, or copper
Gregg Reference Manual (1993)
When three or more items are listed in a series, and the last item is preceded by and, or, or nor, place a comma before the conjunction as well as between the other items.
CON serial comma
 AP Stylebook (2009)
Use commas to separate elements in a series, but do not put a comma before the conjunction in a simple series:
The flag is red, white and blue.
He would nominate Tom, Dick or Harry.
AP does allow a comma before and when ambiguity would result without one:
Put a comma before the concluding conjunction in a series, however, if an integral element of the series requires a conjunction:
I had orange juice, toast, and ham and eggs for breakfast.
Penguin Guide to Punctuation (1997)
Note also that it is not usual in British usage to put a listing comma before the word and or or itself (though American usage regularly puts one there.) So, in British usage, it is not usual to write The Three Musketeers were Athos, Porthos, and Aramis.
On the fence regarding the serial comma
Penguin Writer’s Manual (2002)
It is becoming more common in British English (and is usual in American English) to place a comma before the and that precedes the final item in a simple list (numbers one, two, three, and four).
Fowler’s Modern English Usage (1965)
In promoting the use of the serial comma, CMOS observes that the usage is “blessed by Fowler” among other authorities. However, when I looked up the topic in Fowler (1965 edition) I found this remark, which seems neutral at best:
The more usual way of punctuating such an enumeration as was used as an example in the preceding section is French, German, Italian and Spanish; the commas between French and German and German and Italian take the place of ands; there is no comma after Italian because, with and, it would be otiose [having no practical function; redundant; superfluous]. There are, however, some who favour putting one there, arguing that, since it may sometimes be needed to avoid ambiguity it may as well be used always for the sake of uniformity.
So there you have it. My choice is to travel the path of otiosity for the sake of uniformity. What’s yours?

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