When I was learning grammar, the rule concerning commas and
lists was easy. In any list, and a list was defined as having three or more
items, you put a comma between each item, including before the “and”. In other
words, your list liked like this: “I need to go to the store to buy milk, eggs,
butter, and cheese.”
When my daughter went to school, they taught her to omit the
comma before the “and”, making the list look like this: “I need to go to the
store to buy milk, eggs, butter and cheese.” This works well, unless the last
two items on the list could be mistaken for a single item. For example, what if
my list was slightly different? “I need to go to the store to buy milk, eggs,
butter, macaroni and cheese.” Do I need to buy both cheese from the dairy case
and macaroni from the pasta aisle, or am I looking for a box of macaroni and
cheese from the prepared foods aisle? My daughter’s teacher told me that the
comma belonged before the “and” only if there was some
ambiguity in the list.
Out of habit, I continued to always put the comma before the
“and”. None of my college teachers have objected to its presence. When I sat
down to write this post, I decided to do a little research and find out the
current rule of correct comma usage. I searched at least a dozen sources, and
found a great deal of confusion. No one seems to agree whether to put the comma
in before the “and”, or not. Some sources said the comma should absolutely be
there, while others said it should only be included in cases of ambiguity.
There didn’t seem to be a clear difference between US and UK rules. Finally, I
found a resource from the University of North Carolina which seems to be the
final authority. They say, “Put commas between items in a list. When giving a
short and simple list of things in a sentence, the last comma (right before the
conjunction–usually “and” or “or”) is optional, but it is never
wrong. If the items in the list are longer and more complicated, you should
always place a final comma before the conjunction.”
I’ll keep adding that final comma out of habit, but it’s
good to know that while it is optional, it is never wrong.
~Marie