Run-on sentences and comma splices consist of two or more main clauses (each containing a subject and a verb and able to stand alone as a sentence) that are not joined correctly, making them ungrammatical and hard to follow. In a run-on sentence, the main clauses are just stuck together:

In a comma splice, a comma — and only a comma — comes between the main clauses:

Run-ons and comma splices make the writer look sloppy. If you are prone to writing run-ons or comma splices, you may want to review the discussion of standard sentence structures. To avoid problems with run-ons and comma splices, you need to be able to recognize main clauses. Once you can pick them out, solving the problems is simple. You have four options.