Should You Use Commas, Yes or No?

Comma Rule #3
Place commas before a coordinating conjunction that joins two independent clauses.

Ask yourself, "What is the conjunction joining?"

1. Two words (like two nouns or verbs or adjectives)? —No comma!
 
We did not eat nor sleep for five days.
2. Two phrases (like prepositional or participle or infinitive phrases)? —No comma!
 
The road runs through the valley and up the mountain.
3. Two dependent clauses (adjective clauses or adverb clauses or noun clauses)? —No comma!
 
The tourists were forced to cut their vacations short because a hurricane was approaching the coast and because rebel terrorists were threatening to destroy the airport.
4. Two independent clauses (which could stand on their own as sentences)? —Yes! Place a comma before the coordinating conjunction.
 
The inspectors discovered that the library ceiling contained asbestos, but the school could not afford to have the material removed.
5. Three or more words, phrases, or clauses? —Yes, follow the rule for putting commas between items in a series.
 
The student assistant may need to consult the lab manual, the operational instructions, or the technician.

Click HERE to compare your answers (to the exercises, pp. 233-34) to the instructor's answers.