Before we get to the problems and how to fix them, let’s take a minute to review some information that is so basic you’ve probably forgotten it.
What is a complete sentence? A complete sentence is not merely a group of words with a capital letter at the beginning and a period or question mark at the end. A complete sentence has three components:
Some sentences can be very short, with only two or three words expressing a complete thought, like this:
They waited.
This sentence has a subject (They) and a verb (waited), and it expresses a complete thought. We can understand the idea completely with just those two words, so again, it’s independent—an independent clause. But independent clauses (i.e., complete sentences) can be expanded to contain a lot more information, like this:
They waited for the bus all morning.
They waited for the bus all morning in the rain last Tuesday.
Wishing they’d brought their umbrella, they waited for the bus all morning in the rain last Tuesday.
Wishing they’d brought their umbrella and dreaming of their nice warm bed, they waited for the bus all morning in the rain last Tuesday, determined to make it to class for their test.
As your sentences grow more complicated, it gets harder to spot and stay focused on the basic elements of a complete sentence, but if you look carefully at the examples above, you’ll see that the main thought is still that they waited—one main subject and one main verb. No matter how long or short the other sentence parts are, none of them can stand alone and make sense.
Being able to find the main subject, the main verb, and the complete thought is the first trick to learn for identifying fragments and run-ons.
A sentence fragment is an incomplete sentence. Some fragments are incomplete because they lack either a subject or a verb, or both. The fragments that most students have trouble with, however, are dependent clauses—they have a subject and a verb, so they look like complete sentences, but they don’t express a complete thought. They’re called “dependent” because they can’t stand on their own (just like some people you might know who are SO dependent!). Look at these dependent clauses. They’re just begging for more information to make the thoughts complete:
Because their car was in the shop (…What did they do?)
After the rain stops (…What then?)
When you finally take the test (…What will happen?)
Since you asked (…Will you get the answer?)
If you want to go with me (…What should you do?)
Does each of these examples have a subject? Yes. Does each have a verb? Yes. So what makes the thought incomplete? It’s the first word (Because, After, When, Since, If). These words belong to a special class of words called subordinators or subordinating conjunctions. If you know something about subordinating conjunctions, you can probably eliminate 90% of your fragments.
First, you need to know that subordinating conjunctions do three things:
Second, you need to recognize the subordinators when you see them. Here is a list of common subordinating conjunctions and the relationships they indicate:
Third, you need to know that the subordinator (and the whole dependent clause) doesn’t have to be at the beginning of the sentence. The dependent clause and the independent clause can switch places, but the whole clause moves as one big chunk. Look at how these clauses switched places in the sentence:
Because their car was in the shop, they took the bus.
They took the bus because their car was in the shop.
Finally, you need to know that every dependent clause needs to be attached to an independent clause (remember, the independent clause can stand on its own).
How do you find and fix your fragments? Remember the basics: subject, verb, and complete thought. If you can recognize those things, you’re halfway there. Then, scan your sentences for subordinating conjunctions. If you find one, first identify the whole chunk of the dependent clause (the subject and verb that go with the subordinator), and then make sure they’re attached to an independent clause.
They took the bus. (Independent clause. So far, all is well!)
Because their car was in the shop. (Dependent clause all by itself. Uh oh! Fragment!)
They took the bus because their car was in the shop.
These are also called fused sentences. You are making a run-on when you put two complete sentences (a subject and its predicate and another subject and its predicate) together in one sentence without separating them properly. Here’s an example of a run-on:
My favorite Mediterranean spread is hummus it is very garlicky.
This one sentence actually contains two complete sentences. But in the rush to get that idea out, I made it into one incorrect sentence. Luckily, there are many ways to correct this run-on sentence.
You could use a semicolon:
My favorite Mediterranean spread is hummus; it is very garlicky.
You could use a comma and a coordinating conjunction (for, and, nor, but, or, yet, so):
My favorite Mediterranean spread is hummus, for it is very garlicky. -OR- My favorite Mediterranean spread is hummus, and it is very garlicky.
You could use a subordinating conjunction (see above):
My favorite Mediterranean spread is hummus because it is very garlicky. -OR- Because it is so garlicky, my favorite Mediterranean spread is hummus.
You could make it into two separate sentences with a period in between:
My favorite Mediterranean spread is hummus. It is very garlicky.
You could use an em-dash (a long dash) for emphasis:
My favorite Mediterranean spread is hummus—it is very garlicky.
NOTE: You CANNOT simply add a comma between the two sentences, or you’ll end up with what’s called a “comma splice.” Here’s an example of a comma splice:
My favorite Mediterranean spread is hummus, it is very garlicky.
You can fix a comma splice the same way you fix a run-on—either change the punctuation or add a conjunction. The good news is that writers tend to be either comma splicers or run-on artists, but almost never both. Which one are you? If you have particular trouble with comma splices, try looking at our handout on commas.
As you can see, fixing run-ons is pretty easy once you see them—but how do you find out if a sentence is a run-on if you aren’t sure? Rei R. Noguchi, in his book Grammar and the Teaching of Writing, recommends two methods for testing your sentences. Try these two tests:
These are two things that nearly everyone can do easily if the sentence is not a run-on, but they become next to impossible if it is.
Look at the following sentence:
My favorite Mediterranean spread is hummus.
If you turn it into a question that someone could answer with a yes or no, it looks like this:
Is my favorite Mediterranean spread hummus?
If you turn it into a tag question, it looks like this:
My favorite Mediterranean spread is hummus, isn’t it?
The first sentence is complete and not a run-on, because our test worked.
Now, look again at the original run-on sentence:
My favorite Mediterranean spread is hummus it is very garlicky.
The yes/no question can only be made with each separate thought, not the sentence as a whole:
Is my favorite Mediterranean spread hummus? Is it very garlicky?
But not:
Is my favorite Mediterranean spread hummus is it very garlicky?
The tag question can also only be made with each separate thought, rather than the whole:
My favorite Mediterranean spread is hummus, isn’t it? It’s very garlicky, isn’t it?
But never:
My favorite Mediterranean spread is hummus it is very garlicky, isn’t it?
Unlike the complete sentence, the run-on sentence doesn’t pass these tests. When you try to turn the run-on sentence into a single question, you immediately see that the sentence has more than one complete concept. Make sure you try both tests with each of your problem sentences, because you may trick yourself by just putting a tag on the last part and not noticing that it doesn’t work on the first. Some people might not notice that “My favorite Mediterranean spread is hummus it is very garlicky isn’t it?” is wrong, but most people will spot the yes/no question problem right away.
Every once in a while, you or your instructor will see a really long sentence and think it’s a run-on when it isn’t. Really long sentences can be tiring but not necessarily wrong—just make sure that yours aren’t wrong by using the tests above.
We consulted these works while writing this handout. This is not a comprehensive list of resources on the handout’s topic, and we encourage you to do your own research to find additional publications. Please do not use this list as a model for the format of your own reference list, as it may not match the citation style you are using. For guidance on formatting citations, please see the UNC Libraries citation tutorial. We revise these tips periodically and welcome feedback.
Hacker, Diana, and Nancy Sommers. 2014. A Writer’s Reference, 8th ed. Boston: Bedford/St Martin’s.
Lunsford, Andrea A. 2015. The St. Martin’s Handbook, 8th ed. Boston: Bedford/St Martin’s.
Noguchi, Rei. 1991. Grammar and the Teaching of Writing: Limits and Possibilities. Urbana, IL: National Council of Teachers of English.
Ruszkiewicz, John J., Christy Friend, Daniel Seward, and Maxine Hairston. 2010. The Scott, Foresman Handbook for Writers, 9th ed. Boston: Pearson Education.
The Writing Center at the University of North Carolina, Fragments and Run-ons.