by David Becker
This week we address the serial comma, seventh in the list of the Top 10 most common APA Style errors as identified by Onwuegbuzie, Combs, Slate, and Frels (2010).
Also known as the Oxford comma, the serial comma is the final comma in a list of three items or more, and it is used immediately before and, or, and occasionally nor. For example, if Simon & Garfunkel had recorded their classic album Parsley, Sage, Rosemary and Thyme under APA Records, which doesn't actually exist, then that album would have been titled Parsley, Sage, Rosemary, and Thyme with the serial comma included. This rule also applies to parenthetical citations, in which ampersands are used in place of the full word and. For instance, one would say (Lennon, McCartney, Harrison, & Starr, 1964) instead of (Lennon, McCartney, Harrison & Starr, 1964).
There are various aesthetic and technical arguments for why serial commas should or should not be used. Although they aren’t required in journalistic writing, a distinct advantage of using serial commas is clear, unambiguous language, which is a necessity in scientific 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.
For more information about commas and their proper usage in APA Style, see pages 88 and 89 of the Publication Manual, Sixth Edition (4.03 Comma). Also, pages 63–65 go into greater detail about creating lists (3.04 Seriation). You may also find it helpful to read two previous APA Style blog entries about creating lists: one on parallelism and another on commas and semicolons.