When a noun is preceded by two or more adjectives, sometimes commas are used to separate the adjectives and sometimes they are not. How can you tell when to use commas and when not to? There are a couple of handy tricks to help you figure this out.
When two or more adjectives modify a noun separately, they are called coordinate adjectives. An easy way to tell whether you’re dealing with coordinate adjectives is to insert and between them—if the meaning of the phrase doesn’t change, you’ve got coordinate adjectives, and you should separate them with commas. Alternatively, coordinate adjectives can be rearranged without altering the meaning of the phrase:
Danielle has young, good-looking, hip friends.
Danielle has young and good-looking and hip friends.
Danielle has hip, good-looking, young friends.
However, two or more adjectives that do not modify a noun separately are called cumulative adjectives. Cumulative adjectives piggyback on one another, each modifying the rest of the word group that follows it. They cannot be separated by and or rearranged without changing the meaning of the phrase:
Danielle has many young friends.
Here, young modifies friends, but many modifies young friends. You wouldn’t be able to write many and young or young, many without altering your meaning or just not making sense.
Could You Repeat That?
If the same adjective is repeated for emphasis, use a comma:
Danielle has many, many friends.
Do you have a question about the comma? Let me know, and I’ll include it in a future installment of Mots Justes’ ongoing series.
The Mots Justes Series on Commas
Part I—To Serialize or Not to Serialize
Resources
Chicago Manual of Style, The. 15th ed. Chicago: The University of Chicago Press, 2003.
Fogarty, Mignon, Grammar Girl’s Quick and Dirty Tips for Better Writing. New York: Holt Paperbacks, 2008.
Hacker, Diana, The Bedford Handbook for Writers, 3rd ed. Boston: St. Martin’s Press: 1991.
Mots Justes 
Pingback: Sunday Wash-Up 16th August « Shack's Comings and Goings