- When a comma or no punctuation is used between two complete sentences, the result is referred to as a "run-on" sentence.
The vacuum tube burned out, it will be replaced.
The computer is down, you must fix it soon.
- When two or more independent clauses not joined by a conjunction (and, but, for, when, as, because, or though) are to form a single sentence, they must be separated by a semicolon or period
The vacuum tube burned out; it will be replaced soon.
The computer is down. You must fix it soon.
- Or you can join the the independent clauses with a comma follow by a conjuction:
The vacuum tube burned out, but it will be replaced.
The computer is down, and you must fix it soon.