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 (see bibliog. 1,2), since it prevents ambiguity.Examples of such potential ambiguity are easy to imagine: "With gratitude to my parents, Mother Teresa and the pope." Newspapers see it otherwise. The Associated Press has a "don't use it ... unless you need to use it" approach:
Q: Is clarity essentially the only rule determining when a serial comma should be included?As does the New York Times, whose deputy news editor offers:
A: In a simple series, AP doesn't use a comma before the last item. For a series of complex terms, though, use commas after each for clarity.
I haven't researched the question, but I suspect that journalists' aversion to the additional comma arose in the old days when setting type was laborious and expensive. If you already have an "and," why bother with a comma, too? The practice persists, from habit and perhaps from the sense that fewer commas make prose seem more direct and rapid — qualities we journalists prize in our writing.The Economist concurs: "Do not put a comma before and at the end of a sequence of items unless one of the items includes another and. Thus 'The doctor suggested an aspirin, half a grapefruit and a cup of broth. But he ordered scrambled eggs, whisky and soda, and a selection from the trolley.'"
There are a few cases, however, where we have to make an exception for clarity. For example: The candidate promised lower taxes, higher spending, and ice cream and cake. Without a comma after "spending," the sentence would be a jumble.
In Eats, Shoots & Leaves, Lynne Truss wrote: "There are people who embrace the Oxford comma, and people who don't, and I'll just say this: never get between these people when drink has been taken." A poll has been posted, and it's time to throw down.