Explanation:
A. Run-ons, for instance, require only that you see to it every independent verb has a period or conjunction between it and the next independent verb.
B. Fragments, are equally easy to correct. Just make sure every sentence you write has its own independent verb.
What's an independent verb? "Verbs are independent if they function as the main verb of a sentence, which means that the clauses they're in can stand alone and still make sense." For instance, in the sentence you just read, the verb is an independent verb, while all the others (function, means, they're, can stand, and make) are dependent. You can see the difference for yourself if you say just the dependent clauses by themselves: "if they function as the main verb of a sentence," "which means," "the clauses they're in," "that the clauses . . . can stand alone," "and still make sense." None of these separate clauses makes sense on its own, while "Verbs are independent" does. That makes "Verbs are independent" a full sentence with an independent verb. [Dependent clauses are introduced most often by subordinating conjunctions like "which," "since," "when," "although," and the like.]
Using your natural instincts about the language, you can learn to recognize the difference. If, for instance, I were to say "What you did" and left it at that, you'd be confused about what I meant because "What you did" is not a full sentence. It's a fragment. If, however, I were to say "What you did is good!," I've turned the fragment into a full sentence by adding an independent verb, "is (good)." Now you're no longer confused about my meaning. Thus, all I'm asking for here is that you pay attention to what you already do automatically whenever you talk, think, or listen.
While simple things to correct, run-ons and sentence fragments can leave behind quite a negative impression of your writing, something you want to avoid especially in academic prose.
When you are reading along in a sentence, I mean, and you just never seem to get to the main verb which is absolutely essential to any sentence, instead, you can't see the writer's point because you can't figure out what the main sentence is since you're stuck in some dinosaur of a clause that is lumbering all over the place and not headed anywhere, and so you begin to forget what the writer's talking about because it has been so long since he last mentioned it that who could remember back that far back anyway except maybe Einstein or some memory genius but not a poor teacher who has a big stack of papers to read and has to evaluate them in terms of what this person or that person has or has not learned, you know. For example, students' papers.
The first sentence (everything up to "you know" near the end) is a run-on, and the second ("For example, students' papers.") is a fragment. As a result, neither sentence makes good sense on its own, and reading both is difficult.
Actually both sentences above are fragments—neither has a main verb—so it's not necessarily true that all run-on sentences are long or all sentence fragments are short.
Run-ons can be relatively short and have many conjunctions like "and" or "but" or "yet" and still include too many things in that one small sentence for the reader to follow easily and grasp and digest and understand what the writer is saying and means. On the other hand, fragments that are a common problem especially since students tend to write as they speak and colloquial speech frequently includes fragments, such as answers to questions in which a full sentence is implied by a one- or two-word answer, like "How are you?" "Fine" (implying "<I am> fine."), but in writing a paper which is not a dialogue where such ellipsis (that is, the omission of words that are implied) is not possible because the reader is not filling in the writer's words with grammar from his own speech, which is just the different natures of writing and speaking.
Here the first, shorter sentence is a run-on (from the beginning through ". . . is saying and means.") and the second, longer one (from "On the other hand, . . ." to the end of the paragraph) is a fragment—and also a run-on, I suppose.
If I sound to you like the punctuation police again, let me end by saying that students are not the sole or even worst criminals on record when it comes to run-ons and fragments, not by a long shot. Scholars and professors, for instance, are among the most notorious perpetrators of run-on sentences, because a lengthy thought is often presumed, in and of itself, to be a weighty one—a grossly false assumption since short sentences can carry weight.
Hope this helped you!
