"When To Use Commas" Oregon State Guide to Grammar

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When to Use Commas - Transcript
Written by J.T. Bushnell, Oregon State University Senior Instructor of English
Performed by Rachael Higham

There are few grammar issues that cause more headaches than commas. They’re so common that no writer can escape them, but they’re also commonly misunderstood.

Our students often ask if they’re using too many commas, or maybe not using enough. Or they ask whether a pause is substantial enough for a comma. But these are the wrong questions. You use as many commas as your writing calls for, and commas coincide with some pauses but not with others. The right question is, what are commas for? Where do we need them?

The answer takes us back to the 1400s, when the modern comma, that little curve at the bottom of a line of type, was invented by an Italian printer to separate items within a sentence. That’s still largely their purpose today. Primarily, commas separate three kinds of items: elements in a list, parentheticals, and independent clauses.

Another name for a list is a series, and so we call the commas that separate the elements of a list “serial commas.” They’re useful for showing where one item ends and another begins. That way, a lemon, lime, and orange doesn’t sound like a lemon lime and orange. The length of the pause doesn’t change that. Neither does the number of commas already on the page.

Parentheticals are extra bits of information you jam into a sentence, the kind of thing that could go in parentheses, which is where the construction gets its name. The lime, a very sour fruit, is given to the baby. We know it’s an extra bit of information because without it, the sentence would work just fine and have the same meaning. So we show that by using commas to separate the extra information – one on each side, just like with parentheses. We use these commas when we address someone directly, dear viewers, add a state after a city, and add a year after a date. Those are all parentheticals and need both commas.

When it comes to clauses, the rules are a little bit more complicated, but the basic version is this. Whenever you begin a new independent clause in the middle of a sentence, you need a comma first. The comma helps to separate that new independent clause from whatever came before it. An example of an independent clause would be, “The baby puckers.” Well, if we want to put an introductory word before it, we use a comma. Yes, the baby puckers. If we want to put a phrase before it, we use a comma: After a moment, the baby puckers. If we want to put a dependent clause before it, we use a comma: When he eats a lemon, the baby puckers. And if we want to put an independent clause before it – you guessed it – we use a comma. The baby eats lemon, and the baby puckers.

But you might notice that we added something else that time: “and.” When you separate two independent clauses with a comma – “The baby eats lemon,” “the baby puckers” – you need a coordinating conjunction between them: “and,” “or,” “but,” or “so.”  The comma goes before the coordinating conjunction. That’s the rule, whether we pause or not, and no matter how many commas are already on the page.

View the full series:

The Oregon State Guide to Grammar