Commas with the vocative case
Commas are used to show the vocative case.
(also covered in the lesson Vocative Case)

Commas and the Vocative Case

When addressing someone directly, writers should separate the name being used (e.g., John, Mary, my darling, you little rascal, my son) from rest of the sentence using a comma or commas.


Alan, put your hand up if you do not understand.
(Alan is being addressed. The word Alan is said to be in the vocative case. It must separated from the rest of the sentence with a comma.)

Where do you think you are going, you little devil?
(Somebody is being addressed as you little devil. Those words are in the vocative case, and a comma is required.)

Absolutely, John, get your skates on.

When somebody is being addressed directly, his/her name must be separated from the rest of the sentence with a comma (or commas).

Names that are being addressed directly are said to be in the vocative case.

See also:

What is the vocative case?
Commas after a sentence introductions
Commas after a transitional phrase
Commas after interjections (yes, no, indeed)
Commas before conjunctions (and, or, but)
Commas for parenthesis
Commas in lists
Commas with a long subject
Commas with numbers
Commas with quotation (speech) marks
List of easily confused words