A background knowledge about several types of clauses is not only essential for determining when to use commas, but also for the construction of effective and grammatically accurate sentences. Here are a few quick, key terms to look for, as defined by the Purdue OWL:

Independent Clause: A group of words that contain a subject and verb and expresses a complete thought. An independent clause also could be called a complete sentence.

Dependent Clause: A group of words that contain a subject and verb but does NOT express a complete thought. A dependent clause is marked by one of these words: after, although, as, as if, because, before, even if, even though.

Parenthetical Clause: A group of words that provides additional information tha is not essential to the structure of the sentence. If the clause can be ommitted from the sentence and the structure of the sentence is the same, then it is parenthetical.

Introductory Clause: A dependent clause that provides background information before the independent clause.

Conjunction: Words used as connecting word at the beginning of an independent clause. Some examples are and, but, for, or, nor, so, and yet.


These five handy tips adapted from the Hamilton University Writing Center can help guide your usage of commas:

Use a comma after an introductory clause.

According to Smith, the review session is tomorrow at seven.

Use commas before and after a parenthetical clause.

Smith, the new teaching assistant, was not at class yesterday.

Use a comma to separate two independent clauses linked by a conjunction.

Smith promised to share the notes on Brightspace, but he has not posted them yet.

Use a comma to separate items in a list.

Watching sports, dancing, and studying are Smith's favorite activities.

Use a comma before a quotation when a word like 'say' precedes the quotation.

Smith exclaimed, "That's a lot of homework!"


Adapted from: Hamilton University WC & Purdue OWL