Basic Rules for Comma Usage
- Use a comma before a coordinating conjunction (and, but, or, nor, for, and yet) that joins sentences.
I adjusted the camera lens, and I took an amazing photograph.
- Use a comma to separate items in a series (of nouns, verbs, adjectives, prepositional phrases).
Jamar researched careers in education, law, and medicine.
- Use a comma after some introductory words and word groups (interjections, sub clauses)
Fortunately, I made a backup.
- Use commas to set off most interrupting words and expressions (noun of direct address, appositives, interrupting word/expression).
The ump’s decision, in my opinion, was fair.
NOTE: When two or more adjectives precede a noun or pronoun, a comma is often—but not always—necessary. If you can switch the order of the adjectives or you can replace each comma with and, then the commas are necessary.
It was a joyous, tearful reunion. (necessary)
I’ll wear the old red shirt. (not necessary)
WHAT IS A COMMA SPLICE?
Comma Splice: A specific kind of run-on sentence. A comma splice results when two or more sentences are joined with only a comma.
A comma by itself cannot properly join, or splice together, two sentences.
Example: I woke up late this morning, I couldn’t get to school on time.
* This sentence contains a comma splice because “I woke up late this morning” and “I couldn’t get to school on time” could both be sentences on their own.
How to fix it?
1. Separate the sentences with an end mark or semicolon.
Example: I woke up late this morning; I couldn’t get to school on time.
2. Add a conjunction.
Example: I woke up late this morning, and I couldn’t get to school on time.
3. Revise one sentence to be a subordinate clause properly joined to the other sentence.
Example: After I woke up late this morning, I couldn’t get to school on time.