Conventions of Composition Rule 1
Rule: Two independent clauses joined by for, and, nor, but, or, yet, or so need to be separated by a comma.
Examples:
Wrong: I wanted to play basketball but I can't shoot a jump shot.
Better: I wanted to play basketball, but I can't shoot a jump shot.
Wrong: Everyone loves Grammar Gateways so the English Department offers four per year.
Better: Everyone loves Grammar Gateways, so the English Department offers four per year.
Practice punctuating the sentences below, deciding if and where they need commas:
His parents gave him everything so he ended up spoiled.
They helped out when they could and where they could.
I read the assignment and my teacher gave a quiz on it.
Ryan had rejected the offer twice yet Jaime kept asking her.
Richard should study on his own or Pattie can teach him the rules.
Resources for more explanation of how to punctuate sentences that use coordinating conjunctions:
Purdue OWL's Independent and Dependent Clauses
Purdue OWL's Conquering the Comma
Purdue OWL's Commas
The Writing Center at UNC-Chapel Hill's Commas