Run-ons and Comma SplicesRun-ons and comma splices occur when a writer does not know when one main clause ends and another begins. They are groups of words which ought to be two separate sentences or a single sentence joined in a new way. Students write run-ons when they have two closely related thoughts in their heads. The logical closeness of the thoughts makes seeing that they are separate sentences difficult.
The only difference between run-ons and comma splices is a comma. A run-on is two sentences joined without any intervening punctuation (Desi likes Lucy Fred likes Ethel.). A comma splice is two sentences mistakenly joined by only a comma (Desi likes Lucy, Fred likes Ethel.).
Words like "therefore," "however," and "in fact" are common sources of problems. These transitional words and phrases should begin new sentences. They are not like the subordinating conjunctions ("since," "if," "because," etc.).
To correct run-on errors either put a period in between the two sentences or figure out how the clauses are related and combine the sentences into a single sentence (Desi likes Lucy. Fred likes Ethel. -- or -- Desi likes Lucy, but Fred likes Ethel.)
Often combining the sentence means making one of the main clauses a phrase or subordinate clause (Though Desi likes Lucy, Fred likes Ethel.).
How to Fix Run-Ons and Comma Splices:
Note: Run-ons have nothing to do with the length of a sentence. Long sentences maybe wordy or rambling, but that does not mean they are run-ons.