OVERVIEW

A comma (,) is punctuation that separates parts of a sentence and tells readers to pause briefly.

When to use (or not to use) commas is one of the most challenging aspects of written English. This unit covers the most common or most bothersome types of errors involving commas.

Some comma lessons are interrelated with other units. For more information on using a comma to join independent clauses—word groups with subjects and verbs—see the units on run-ons, coordination, and conjunctions.

WATCH EXAMPLES

The first video describes the major uses of the comma:

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The second video describes unnecessary uses of the comma. Commas are not needed in these situations:

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READ EXAMPLES

Commas and Conjunctions

A comma and a conjunction can be used to join two independent clauses, as in this example.

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To correctly join the two independent clauses in one sentence, a comma is needed before the coordinating conjunction. Without this correctly placed comma, the sentence is a run-on.

Commas and Introductory Elements

In addition, commas set off introductory elements from the main clause in a sentence. In particular, a comma is needed when a sentence begins with a subordinating conjunction; this comma marks the shift from the subordinate clause—a clause with a subject and a verb that cannot stand alone--to the independent clause, which can stand alone.

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The comma that follows the subordinate clause Because I was in a hurry sets that clause off from the main clause I had no time to call you.

Not all introductory elements require a comma; sometimes these commas are optional. Even so, placing commas after the last word of the introductory element and before the first word of the main clause is a good strategy for avoiding comma errors.

Commas and Transitional Terms

Commas also set off transitional terms from the main sentence. A transitional term (often called a conjunctive adverb) clarifies the relationship between two independent clauses. The transitional term however helps readers understand just how closely connected these two ideas are.

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As described above, commas and conjunctions can join independent clauses, but a comma and a transitional expression cannot. This correction involves joining the two independent clauses with a semicolon. A comma is usually placed after the transitional term, which helps readers notice the shift to the main clause.

Commas and Nonessential Clauses

Commas are also needed to set off word groups that are not as important as the main clause for understanding the meaning of a sentence.

If the clause does not significantly alter the meaning of the noun it modifies, it is said to be nonessential to the meaning of the sentence. A nonessential adjective clause should be separated from the rest of the sentence with commas.

Another type of clause that is sometimes separated from the main clause by commas is an appositive. Appositives are nouns or pronouns that rename or modify the nouns they follow.

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The correction shows that a comma is needed since the appositive is nonessential. Describing Julia as my aunt is not essential for understanding the sentence. The appositive does not significantly alter the meaning of the noun it renames, and it should be set off with commas.

Unnecessary Commas

Commas are not needed in these situations:

Below are examples of errors with unnecessary commas.

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The comma comes before but not after the coordinating conjunction but.

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A single comma should never come between a subject and a verb. In the example above, the subject is fly and the verb is is. long. Even though there are words between the subject and verb, there is no rule requiring those words to be set off with commas, so the comma before is is incorrect.

A comma is unnecessary before a list. Commas are required between the items in a series, but a comma does not introduce the list, as shown in the correction below.

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CONTINUE THROUGH THE UNIT

The study pages provide more details about when to use and when not to use commas. As you read through the study pages and then practice with LearningCurve, try to ask these questions:

Answering these questions will help you identify and correct comma errors for the post-test (if assigned) and in your own writing.

Don’t forget to work smartly!