Comma Splice or Run-on Sentence

You cannot connect two INDEPENDENT clauses with a comma. It is called a comma splice. You have to use either a semicolon or a comma with a coordinating conjunction(And, but, for, nor, or, so, and yet) or write them as separate sentences. Examples:
Incorrect: He was sick, he couldn't come.
Correct: He was sick, so he couldn't come.
Correct: He was sick; he couldn't come.
Correct: He was sick. He couldn't come.