THE OXFORD COMMA.
What is this little beast? The US has adopted it as a favourite son, so, if you live in Australia or Britain, and have a grammar checker made in the US - be warned - you will be told repeatedly that you have made an error by leaving out a comma.
THE CRUCIAL DIFFERENCE So, the sentence below illustrates standard punctuation in Britain and Australia. Jim offers critiques, editing and mentoring.
In the US, this sentence would be written: Jim offers critiques, editing, and mentoring.
That comma after 'editing' is known as the Oxford comma. It is named for the Oxford University Press, which is the single British style guide that recommends it. The rest don't. The US publishing industry does favour it, so when I edit for an American author or publication, I have to ensure I use it ... and with US spellings throughout, of course.
WHAT IS THE VALUE OF THE OXFORD COMMA? The argument FOR the Oxford comma is that it prevents ambiguity. There are a few instances where, yes, it is vital to use that extra comma. For example, in this sentence:
I would like to thank my parents, Professor Blake and Dolly Parton. In the example above, the lack of a comma after Professor Blake makes it sound as if the speaker's parents are the professor and Dolly. The addition of the Oxford comma makes it perfectly clear we are talking about 3 separate entities... parents, professor, and Dolly Parton. Now, that makes absolute sense to me. Of course we need a comma in such a situation.
SO WHY DON'T WE ALWAYS USE AN OXFORD COMMA?
In the US, the Oxford comma is applied as standard. BUT, why do we need to apply it relentlessly to every series, even when there is no ambiguity? To my eye, the sentence: 'He only eats salmon, tuna, and sardines' seems unnecessarily cluttered and over-precise. The word 'and' is a reasonable stand-in for the comma before it, where there is no chance of ambiguity.
Of course, you need to follow the system favoured by your country or the country where you hope to be published.