The first type of run-on sentence one may encounter is one that fuses two complete sentences by leaving out punctuation marks. If read aloud, most readers should hear the natural break in the sentence, and an incorrect sentence may seem unnatural. Thankfully, this error is easy to fix. First, one should find where the individual sentences begin and end. Remember that a complete sentence must have a subject and an action of some type. When one looks more closely, one can see that a run-on sentence of this type has two subjects and two actions in one undivided sentence. In the example below, the subject of the first sentence is ‘judge’ and the action is ‘sat.’ If one keeps reading, one sees that where the judge sat. If one reads further, the subject of the second sentence, ‘he,’ appears. Now that one knows the second sentence has started, the error is easily fixed. To correct the error, divide these sentences by placing a period after ‘scales.’
INCORRECT: The judge sat on the scales he placed his left hand on the stack of books.
CORRECT: The judge sat on the scales. He placed his left hand on the stack of books.
The second type of run on sentence is one that attempts to properly connect two complete sentences with only a comma. A comma, by itself, is not enough to correctly join two sentences. If only a comma is used to connect two complete sentences, the writer has created a ‘comma splice.’ When connecting two complete sentences in this way, one must include a comma after the end of the first sentence and a coordinating conjunction like ‘and,’ ‘but,’ or ‘or.’ The choice of coordinating conjunction a writer makes should depend on the meaning he or she wishes to convey by connecting the sentences. For example, if the writer wants to show a link between the ideas of the two sentences, ‘and’ is likely the best choice. If the writer wants to show contrast, ‘but’ might work well. In the example below, showing the reader that the ideas of each sentence are somewhat different makes the use of ‘but’ a good choice.
INCORRECT: The gavel in the judge’s hand was very heavy, he did not want to drop it.
CORRECT: The gavel in the judge’s hand was very heavy, but he did not want to drop it.
This type of run-on sentence is like the comma splice, but it also contains an adverb like ‘however’ or ‘therefore’ in the place of a coordinating conjunction. Since these words show a contrast of ideas like ‘but’ or ‘or,’ many novice writers believe that they are used like coordinating conjunctions. These adverbs cannot join with a comma to correctly link two complete sentences. To fix this error, find where the sentences begin and end. In the example below, the commas and adverb break the sentences apart, and the adverb ‘therefore’ shows the beginning of the contrasting sentence. The simplest correction is to change the comma following the first sentence to a semicolon.
INCORRECT: The judge read about a similar case in his books, therefore, he was determined to use this case as a precedent for his own.
CORRECT: The judge read about a similar case in his books; therefore, he was determined to use this case as a precedent for his own.