The punctuation mark comma (,) has the following uses.
To connect the items in a list
Commas are used to connect the items in a list, except for the last two which are usually connected by a coordinating conjunction like and or or.
- My favorite writers are Charles Dickens, Emily Bronte and Jane Austen.
- The Three Musketeers were Arthos, Porthos and Aramis.
To join two complete sentences into a single sentence
A comma is used to join two complete sentences into a single sentence. It is usually followed by a connecting word like and, but, or, while or yet.
- She had very little to live on, but she would never take what was not hers.
Short clauses connected by and, but or or are not usually separated by commas.
- She is poor but she is honest. (NOT She is poor, but she is honest.)
To show that certain words have been omitted
A comma can be used to show that certain words have been omitted.
- Alice decided to order to steak pie and Peter, the chicken pathia. (The omitted words are ‘decided to order’.)
When subordinate clauses begin sentences, they are often separated by commas.
- When the rain stopped, we went out. OR We went out when the rain stopped.
Commas are also used to set off words or expressions that interrupt the natural progression of a sentence
- My friends, however, did not come.
- John had, surprisingly, did everything.