Q. What is a serial comma, and must I use it?
A serial comma is the comma placed before the and or or prior to the final item in a list. It is also known as the Oxford comma and is required in APA (2010) sixth edition style to improve clarity in the writing.
"As an example of how omitting a serial comma can create ambiguity, if I were to say, 'I had lunch with my parents, Barack Obama and the Prime Minister of Australia,' it might seem like Barack Obama and the Australian Prime Minister were my parents, which I can personally assure you is not true. On the other hand, if I were to say, 'I had lunch with my parents, Barack Obama, and the Prime Minister of Australia,' then each of those items is clearly distinct from one another, and Barack Obama and the Australian Prime Minister are no longer my parents, all thanks to the addition of a serial comma" (Becker, 2011).
For More Information
See "Using Serial Commas" (Becker, 2011).
Becker, D. (2011, April 07). Using serial commas [Blog post]. Retrieved from http://blog.apastyle.org/apastyle/2011/04/using-serial-commas.html