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Tools

Comma Usage

A comma is similar to a “yield” sign when you are driving.  Just as a “yield” sign signals the driver to slow down, a comma signals the reader to slow down for understanding. Below, you will find many uses for the comma with examples for each one.

• Separate items in a series (Ex. In the meeting, Aaron asked for budget, tax, and personnel costs.) Although the final comma in a series is optional, we advise you to include it always.
  
  

• Use a comma before the coordinating conjunction in a compound sentence. A compound sentence consists of two independent clauses (each can stand alone). The coordinating conjunctions include and, or, nor, but, yet, so, for. (Ex. She presented her information to the department, and she answered many questions about the data.).




• Comma splice errors occur when you use a comma to connect (or splice) two independent clauses without using a coordinating conjunction.  In the example above, a comma splice error would read, “She presented her information to the department, she answered many questions about the data.”  The comma splice is one of the most common errors in business writing and makes it harder for the reader to decipher your message.
  
  

•  Sentences beginning with because, although, as, and if will use a comma to separate the opening phrase or clause from the rest of the sentence.  (Ex. Because we took a charge against the first quarter’s earnings, we will show a decline in dividends.)  When such clauses or phrases occur at the end of a sentence, you will have to judge whether the clause or phrase is essential to the meaning of the sentence.  If it’s essential, then do not use a comma.  (Ex. We will show a decline in dividends because we took a charge against the first quarter’s earnings.)
  
  

• A comma should follow an interrupting word or phrase at the beginning of a sentence. (Ex. Yes, I can arrange the annual planning meeting for May 25th.)




• A comma should follow an introductory prepositional phrase when the comma helps the reader better understand your message.  Prepositions include under, over, in, before, after, through, between, etc. (Ex. Under the present SEC rules, we must plan carefully to avoid a citation.)
  
  

• Use commas to set off phrases or clauses within the sentence that interrupt the flow of the sentence and that are not essential elements for the understanding of the sentence. (Ex. The board, interviewing steadily for three months, found a replacement for the CEO.)
  
  

• When writing dates in a sentence, use a comma before and after the year. (Ex. The board of directors met on March 2, 2001, with 200 shareholders in attendance.)
  
  

• Use a comma to separate two adjectives that modify the same noun. (Ex. The long, detailed report showed many instances of negligence.)
  
  

• Use commas before and after abbreviations within sentences. (Ex. Rose Patel, Ph.D. has been appointed interim chair of the budget committee.)




•  If you use quoted text within a sentence, use a comma to introduce the text. (Ex. Dr. Epson reported, “Rates of increase hovered around 50% through the past three fiscal years.”

Do not use a comma after the greeting in a business letter. Instead use a colon ( : ).

Compiled for The Goizueta Business Writing Center web site by Deborah Valentine, copyright 2001