The Oxford Comma is attributed to Horace Hart. The printer and controller of the Oxford University Press from 1893 to 1915, Hart authored Hart's Rules for Compositors and Readers in 1905 as a style guide for the employees working at the press. Over time, it gained prominence in various writing communities, especially in the United Kingdom. Its purpose was to bring clarity and prevent ambiguity in complex lists, ensuring that each item was distinctly separated.
And here we get to the nub of it. Consider this sentence:
Mary travelled to Manchester with Peter, a horse, and a clown.
It is obvious here that Mary is travelling with three companions: her friend Peter, a horse, and a clown. Simple, right?
But, if we remove the comma from before ‘and’ (the coordinating conjunction), the sentence is transformed into something much more fantastical and bizarre:
Mary travelled to Manchester with Peter, a horse and a clown.
Technically, this sentence is still correct, but it is possible to infer that Mary only has one travelling companion, a horse called Peter who also happens to be a clown.
Or is that just me?
All right, how about this example?
I would like to thank my parents, Oprah Winfrey and God.
Wow, your parents are Oprah Winfrey and God? That’s amazing! No, wait …
Let’s put that pesky Oxford Comma in there and read that sentence again:
I would like to thank my parents, Oprah Winfrey, and God.
Ah, now that makes so much more sense.
Here is a joke from Benny Hill, reading entries from his diary:
Met Jim Davidson, a fine comedian and a gentleman. Had drinks with all three of them.
The first sentence is structured to mean that Benny Hill met only one person, Jim Davidson, who Hill goes on to describe as a fine comedian and a gentleman. The second sentence reveals that no, it is actually a list of three people, and inferring that Jim Davidson is neither a fine comedian nor a gentleman. In that case our good friend the Oxford comma would have helped clarify the meaning:
Met Jim Davidson, a fine comedian, and a gentleman. Had drinks with all three of them.
There we are, the Oxford Comma enables clarity and precision in our writing, and dispels with the possibility of ambiguity.
But it would have killed that joke.