Use of Comma

Comma Use
1. Use commas to separate independent clauses when they are joined by any of these seven coordinating conjunctions: and, but, for, or, nor, so, yet.
The game was over, but the crowd refused to leave.
The student explained her question, yet the instructor still didn't seem to understand.
Yesterday was her brother's birthday, so she took him out to dinner.
2. Use commas after introductory a) clauses, b) phrases, or c) words that come before the main clause.
a. Common starter words for introductory clauses that should be followed by a comma include after, although, as, because, if, since, when, while.
While I was eating, the cat scratched at the door.
Because her alarm clock was broken, she was late for class.
If you are ill, you ought to see a doctor.
When the snow stops falling, we'll shovel the driveway.
However, don't put a comma after the main clause when a dependent (subordinate) clause follows it (except for cases of extreme contrast).
Incorrect: She was late for class, because her alarm clock was broken.
Incorrect: The cat scratched at the door, while I was eating.
Correct: She was still quite upset, although she had won the Oscar. (This comma use is correct because it is an example of extreme contrast)
b. Common introductory phrases that should be followed by a comma include participial and infinitive phrases, absolute phrases, nonessential appositive phrases, and long prepositional phrases (over four words).
Having finished the test, he left the room.
To get a seat, you'd better come early.
After the test but before lunch, I went jogging.
The sun radiating intense heat, we sought shelter in the cafe.
c. Common introductory words that should be followed by a comma include yes, however, well.
Well, perhaps he meant no harm.
Yes, the package should arrive tomorrow morning.
However, you may not be satisfied with the results.
3. Use a pair of commas in the middle of a sentence to set off clauses, phrases, and words that are not...