1. Commas Commas to Set Off Explanatory Words & Appositives
Commas with Nonrestrictive Phrases & Clauses
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2. Commas to Set off Explanatory Words & Appositives
612.2: Commas are used to enclose an explanatory word or phrase.
Ex. The Dixie Chicks, a crossover musical group, attracts both country and pop music fans.
610.1: A specific kind of explanatory word of phrase called an appositive identifies or renames a preceding noun or pronoun.
Ex. This group has two backup singers to support the lead vocalist, Natalie Maines.

3. Commas with Nonrestrictive Phrases & Clauses
612.2 Nonrestrictive phrases and clauses, sometimes called unnecessary or nonessential word groups, can be removed from a sentence without changing its basic meaning.
Always place commas around nonrestrictive phrases and clauses.
Nonrestrictive example: Auroras, which are displays of light in the sky, can be seen only at night.
Restrictive example: Lights that dance in the night sky are called auroras.

4. Commas: That and Which
Use that to introduce restrictive (necessary) clauses.
The treadmill that monitors heart rate is the one that you must use. (no commas)
Use which to introduce nonrestrictive (unnecessary) clauses.
The treadmill, which we got last year, is required for your program. (commas)

5. Commas: Other Uses 614.1 To Set off Dates
Items in a date: On September 30, 1997, my…
No comma needed for just a month and year: May 2006
Full date in a sentence: On June 7, 1924, my…
614.2 To Set off Items in Addresses
Mail the box to Friends of Wildlife, Box 402, Spokane, Washington
After the state when a city and state are in the middle of the sentence: They are in Juneau, Alaska, for the week.
614.3 In Numbers
Separate hundreds, thousands, millions, and so on: 7,645,268
614.4 To Enclose Titles or Initials
Use commas to enclose a title or initials and names that follow a surname (last name) Letitia O’Reilly, M.D., is our doctor.