Definition of a Run-On
Another type of error that must be avoided when you are constructing sentences is writing run-on sentences. Read this section to learn more about this error and how to identify it.
Despite what it may sound like or what you previously thought it was, a run-on is:
a sentence which contains two or more independent word groups without the proper punctuation and/or connective language.
Keep in mind that much like the definition of a fragment, this definition has nothing to do with the length of a sentence. A run-on can be a very short sentence. Finding run-ons involves being able to look at a sentence and break down how it is put together.
For example, let's look at the following sentence:
My grades are very good this semester my social life rates only a C.
When we break down how it is put together, we find that this sentence contains two independent clauses (I'll highlight the first clause in grey).
My grades are very good this semester my social life rates only a C.
If we go through and find all the subjects and verbs, we find that there are two subjects and two verbs (one subject and one verb in each clause). This means that they are each independent clauses. Although a sentence with multiple subjects and multiple verbs doesn't always mean we are looking at a run-on, if we look more closely at the sentence, we can see that are no words that connect or show a relationship between these subjects and verbs, nor is there any punctuation to correctly attach these independent clauses within one sentence.
Another method that might help you determine that this is a run-on is to read it aloud. When you do this, you will find that there is a hard break between the word "semester" and the word "my." This is where there needs to be some sort of punctuation or connective language.
A type of run-on is something called a comma-splice. Comma splices are simply run-ons that have a comma between the independent word groups.
My grades are very good this semester, my social life rates only a C.
The author here is trying to show a break between the independent clauses, but this is still a run-on because a comma by itself is not a strong enough punctuation to separate two independent clauses (that is, word groups that could stand alone as complete sentences).
Source: Erin Severs
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