(Harvard comma, serial comma, Chicago comma)*
Welcome to the comma wars…
Commas are used to join or separate – depending on your point of view – ideas in a sentence, but arguments abound about the precise rules for their use. In particular, the formal practice of NEVER using a comma when a conjunction is used to terminate a list it items is hotly debated. (Sorry to shout.)
The problem is that the last two items in a list can become linked together when they really have no connection. The unfortunate pairing skews the total meaning of the sentence. An example from Wikipedia uses this apocryphal dedication by an author:
To my parents, Ayn Rand and God.
To my parents, Ayn Rand, and God.
The first suggests that God and Ayn Rand were the parents of the author. The second comma relieves the elephant-in-the-room tension by making clear that there are three separate dedications indicative of normal ancestry and possibly some humility.
At the same source is a newspaper account of a documentary about Merle Haggard:
Among those interviewed were his two ex-wives, Kris Kristofferson and Robert Duvall.
which was probably a surprise to all three men and Haggard’s two ex-wives as well. To make it clear that Kristofferson and Duvall had never married Haggard, let’s re-punctuate:
Among those interviewed were his two ex-wives, Kris Kristofferson, and Robert Duvall.
Consider also this statement:
My usual breakfast is coffee, bacon and eggs and toast.
Should bacon and eggs, or eggs and toast, be grouped together? With a comma after eggs, the foods are:
Coffee + (Bacon and eggs) + Toast
With a comma after bacon:
Coffee + Bacon + (Eggs and toast)
The alternative way of dealing with this kind of ambiguity is to re-arrange the sentence, and that seems to be both counter-productive and a bit twee. American (USA) style guides tend to specify the use of the comma with the terminating conjunction while English sources tend to forbid using both together, according to Wikipedia.
However, the venerable Fowler’s Modern English Usage takes the very commonsense view that the Oxford comma should be used whenever it can make the meaning clearer: and so do I. Clarifying your meaning by inventing another tediously contentious punctuation rule when a perfectly workable solution already exists is plain silly.
* The Oxford University Press stylebook has specified the use of the “serial comma” for some long time and so gives its name to the practice, but there are other candidates with naming rights as well. (Acknowledgements to Wikipedia.)