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The Comma

Comma rules vary greatly depending on the style used, English versus American usage, and other considerations. Here are some general comma rules that apply to a majority of cases. If you’re not sure, check the St. Martin’s Handbook or the recommended style guide.

Use a comma after introductory elements.

Make sure you use a comma after an introductory word, expression, phrase, or clause.
Example: Carefully, the chef added a final touch to his masterful dessert.
Example: To avoid answering the teacher’s question, I sunk into my chair.

Use a comma in compound sentences.

• Use a comma before a coordinating conjunction (and, but, or, for, nor, so, or yet) when it joins two independent clauses (two thoughts that can be complete sentences on their own).
  • Example: The rain began to pound rapidly, and the thunder grew more frequent.

Use commas to set off nonessential elements.

• If the phrase can be taken out of the sentence so that the sentence makes sense without it, set the phrase off with commas.
  • Example: The miners, who went on strike, gained the support of local newspapers.

Use commas to separate items in a series.

• A comma is used in between items in a series of three or more words, phrases, or clauses. You may often see a series with no comma after the next-to-the-last item; however, occasionally omitting that comma can cause confusion, and you will never be wrong if you include it.
  • Example: My favorite foods are pizza, chocolate, and ice cream.

Use commas to set off appositives.

• When an appositive (noun or noun substitute that renames a nearby noun or noun substitute) is not essential to identify what it renames, it is set off with commas.
  • Example: Mrs. Sanders, my childhood piano teacher, taught me to love music.

Use commas to set off contrasting elements.

• Use a comma (or commas) to set off a modifying element that ends or interrupts a sentence if the modifier establishes a contrast.
  • Example: The government chose Texas, not Massachusetts, as the site for the project.

Use commas with adverbial clauses or with that and which clauses.

• Adverbial clauses (when, where, because, although, before) are usually essential to the meaning of the sentence, so they do not need to be set off with commas unless the adverbial clause comes before an independent clause or begins with "although", "even though", "while", or another conjunction expressing the idea of contrast.
• Example: Betty sat in the same chair when she went to the library.
• Example: When Betty went to the library, she always sat in the same chair.
• Example: Betty always sat in the same chair at the library, even though the chair was at the back.
  "That" is always essential and is NOT set of with commas. "Which" can be either essential or nonessential, so the comma rule will depend on the sentence.

Use a comma with quotations.

• A comma at the end of a quoted word, phrase, or sentence goes inside the closing quotation mark.
  • Example: After the play ended, Kelly commented, “I really enjoyed watching my friends on stage.” 

Use commas to set off parenthetical and transitional expressions. 

• Because parenthetical and transitional expressions (any added comments or information) often interrupt or digress, they are usually set off with commas.
  • Example: My dad, of all people, told me not to take school so seriously.

Use commas with dates, addresses, titles, and numbers.

• Dates: Use a comma between the day of the week and the month, between the day of the month and the year, and between the year and the rest of the sentence.
  • Example: On May 12, 2001, Ïã¸Û°ÄÃÅ×ÊÁÏ´óÈ« held graduation exercises.
• Addresses and place names: Use a comma after each part, including the state, if no ZIP code is given. A ZIP code is not preceded by a comma.
  • Example: Ïã¸Û°ÄÃÅ×ÊÁÏ´óÈ« is located at 141 East College Avenue, Decatur, Georgia.
• Titles. Use commas to set off a title such as M.D., Ph.D., and so on, but not with Jr. and Sr.
  • Example: I sent a letter of recommendation to Jane Doe, M.D.
• Numbers. In numbers of five or more digits, use a comma between each group of 3 digits, starting from the right.
• • Example: Currently, the world population is over 7,000,000,000