Commas — the stuff of nightmares? Well, maybe not, but that simple punctuation mark is the most confusing one in English because it has so many different uses. And the uses keep changing over time.

With that said, I’m going to limit this post to a discussion of only one use — the comma with “and.” Even that can be a little confusing because the conjunction “and” can be used to connect everything from items in a grocery list to events in a child’s day.

Let’s get down to specifics. When “and” is used to connect two complete sentences, there is usually a comma before the “and” (never after). Example: The students had to work together on the project in groups of three, and each group had to decide what part of the project to work on.

However — and here comes an exception — when the sentences are short, the comma is often optional. Example: The freshmen are scheduled for orientation on Monday and the sophomores are scheduled for Tuesday. Didn’t I warn you that commas are confusing?

Style books even disagree as to when a comma is optional or not. Take the case of what is referred to as the Oxford comma. That’s a fancy name for the comma used before the “and” in a list. Example: The scientists collected the specimens, cataloged them, and planned their research. The comma after “them” is the Oxford comma. A grammar book from the 1980s described the use of this comma as “old-fashioned.”

Other grammarians have been quick to point out, however, cases in which omitting that final comma in a series sometimes leads to misunderstandings. Here is a humorous example: The young reporter interviewed the senator’s rivals, a prostitute and a bank robber. No problem getting elected with rivals like that! But not all examples are humorous. In this sentence, using or omitting that Oxford comma may make a difference in what kind of treatment a patient receives: The patient needs to be scheduled for physical therapy, massage and whirlpool. Is the patient to receive three different therapies or only two? Since there is a possibility of misunderstanding, I would suggest always using that last comma in a series, just to be safe.

Finally, there is one place you should never use a comma, and that is when the “and” is connecting only two items. Example: That senator supported reproductive rights and gay marriage. The two items can also be longer. Example: My dog ran away one night and didn’t return for a week. If there are only two items and there is not a complete thought on either side of the “and,” then a comma is not needed.

Hopefully, this little discussion helps boost your confidence in using a comma with “and” — or not. If you still have questions, feel free to comment. And stay tuned for more posts about that crazy squiggle called a comma!