Editing Tip: The Basics of Comma Usage

There are many confusing rules about comma usage, and some conventions are up to the writer to decide. Here are some common uses of commas.

The comma (,) is one of the most widely used punctuation marks in the English language. The comma is frequently misused as well, especially because it can be found in so many different situations. Here, we will provide examples and explanations of some of the common ways that a comma is used.

Separating items in a list

Delineating the items in a list may be the most famous use of commas and also one of the most straightforward. Remember that a comma is required to separate all items of a list except the last two. The final comma (sometimes called a serial comma or Oxford comma) is optional: "A, B and C" and "A, B, and C" are both correct.

Delineating nonrestrictive elements in a sentence

Nonrestrictive elements can be omitted without changing the meaning of a sentence, and they are set off from the rest of the sentence with commas. Nonrestrictive elements often begin with the word 'which.' Consider the following example:

  • Uruguay, which won the first FIFA world cup, will play Venezuela later this year. The historical fact about Uruguay is not essential to understand the rest of the sentence, so it is set apart with commas.

Delineating appositives

Appositives are nouns or phrases that provide an alternate name or identity for another noun. When appositives are nonrestrictive, they also require commas:

  • Neil Armstrong, the first American to walk on the moon, was born in Ohio. This nonrestrictive appositive provides additional information that is not critical to the understanding of the sentence, so it should be offset with commas.

Separating independent clauses (along with a conjunction)

An independent clause is a portion of a sentence that could stand alone as a sentence. Independent clauses can be joined together into one sentence with a comma and a conjunction:

  • Three lions wandered past our tent, but we did not run away.
  • There are several types of punctuation marks in English, and each mark has its own usage rules.
    The comma is absolutely required when two independent clauses are conjoined with a conjunction, as in these examples.

Following an introductory clause or dependent clause at the beginning of a sentence

Dependent clauses are descriptive phrases that cannot exist as separate sentences. When they precede the main part of the sentence, they are set off by a comma (as in this sentence). Consider these examples:

  • Because of the high radiation levels, power plant workers were evacuated immediately.
  • Taking all data into consideration, the conclusions were obvious.
    In both of the preceding sentences, the first half could not be its own sentence, so a comma is required. The comma would not be used if the dependent clause came after the independent clause (e.g., "Power plant workers were evacuated immediately because of the high radiation levels.")

Commas can also follow brief introductory phrases to prevent confusion for the reader.

  • In total, twelve different proteins make up this complex.
  • Finally, he could say that his work was done.
    In these cases, the comma is optional but recommended to assist the reader in breaking the sentence into understandable units.

There are other uses for commas, but we hope that this tip has helped to clear up some of the common uses for the comma. If you have questions, please view the rest of our series on commas or contact us. Best of luck with your research and publication!

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