You’ve probably heard a lot of things about the comma. A comma (,) signifies a short pause in a sentence. It can also divide clauses or items in a list. It can be used to create division, or to improve the clarity of a sentence.
Pauses, Adjectives, and Nonessential Phrases
In writing, commas usually signal a pause that would be heard if the sentence were read aloud. It’s a short, soft pause, as opposed to the longer pause signified by a period.
Commas separate adjectives when their order doesn’t affect the meaning of the phrase. For example: “She gave him a soft, comfortable blanket.” The order of the adjectives soft and comfortable could be reversed, so they’re separated by a comma.
In “delicious chocolate cake,” the word chocolate is a direct modifier of cake. So the order of delicious and chocolate shouldn’t be flipped. In this case, the comma isn’t needed.
A comma can also separate nonessential words from the essential parts of a sentence. For example, “Patty came to visit,” doesn’t need a comma. A more specific sentence like “Patty, my second cousin, came to visit,” does need commas to offset the nonessential phrase my second cousin. The information my second cousin isn’t necessary for the sentence to be understandable. In general, commas should be used any time the elements of a single sentence need to be divided.
Numbers and Other Information
YOu can also use commas to divide sets of information. For example, in numbers over 1,000, the comma separates sets of three digits at a time. For example, in 1,000,000, there are two commas, one for every three decimal places.
In a street address, commas divide each piece of information. For example, the address of the Metropolitan Museum of Art in New York is 1000 Fifth Avenue, New York, New York.
The Oxford Comma
Commas also separate items in a list. In a list of 3 or more items, the comma after the second-to-last one is called a serial comma (or the Oxford comma). For example in “He bought eggs, milk, and bread,” there’s a comma between each item listed, including the second-last item. Not all style guides agree whether to use the Oxford comma.
In some cases, you can leave the Oxford comma out without changing the meaning of the sentence. If you omit it from the previous example, it still has the same meaning: “He bought eggs, milk and bread.”
In other cases, the Oxford comma may be necessary to provide clarity. For example, in the sentence “I love my pets, chocolate, and pizza,” the Oxford comma makes it clear that all three items are separate. This one could be confusing if the Oxford comma were left out: “I love my pets, chocolate and pizza,” might mean that the speaker’s pets are named Chocolate and Pizza.