Period to Fix Run-On Sentences and Comma Splices
The Period
Rulebase Summary
Do not join two independent sentences with just a comma when there is no conjunction — this creates a run-on sentence (also called a comma splice). Use a period to separate them into two sentences. If the sentences are closely related, a semicolon is also acceptable.
When a coordinate conjunction (and, but, or, nor) is present, a comma before the conjunction is correct. Parallel constructions (sentences with similar structure) are also not an exception — use a semicolon, not a comma, to join them. When there is no coordinate conjunction between independent clauses, do not use a comma — use a period or semicolon instead.
Examples
A. I went to the front door, nobody answered.
A. I went to the front door. Nobody answered.
Two independent clauses need a period, not a comma.
A. He signed the contract, then he left the office, I stayed behind.
A. He signed the contract. Then he left the office. I stayed behind.
Split run-on into separate sentences with periods.
Style Guide References (2)
BGGP
BGGP