Sentence boundary errors are among the most common errors writers struggle with. They’re called “boundary errors” because they are problems with accurately punctuating sentences so that they are complete–they reach their “boundaries”–and so that they don’t run into one another–don’t “cross boundaries.” They’re such serious errors that sometimes they are referred to as sentence crimes.* There are three major sentence crimes: fragments, comma splices, and run-ons (also called “fused sentences”).
Even good writers have trouble with sentence boundaries. For many writers who have never had trouble with them before, these errors crop up when they begin writing more complicated sentences about more complicated material. If you feel you need to get a better handle on these errors, you are in good company!
Understanding independent clauses
To really understand how sentence boundary errors work, it helps to understand what an independent clause is.
A clause is a group of words that includes a subject-verb pair and additional words or phrases that “complete” the idea. Some clauses are dependent; these start with a word (such as “if,” “because,” or “when”) that makes them unable to stand on their own as sentences. Without this “dependent word” at the beginning (a subordinate conjunction or relative word), a clause is independent.
If the Confederate states had seceded from the Union…
When both agents are applied in tandem…
Because the setting is heavily detailed…
The Confederate states had seceded from the Union.
Both agents are applied in tandem.
The setting is heavily detailed.
If a sentence does not have an independent clause, it is a fragment. Fortunately, a fragment is a very easy problem to solve. Often, a dependent clause or prepositional phrase will be able to attach to either the sentence directly before or after it.
The structure looked fragile. After Jill climbed. Jack climbed as well.
The dependent clause could attach to the independent clause on either side. However, the author likely intended that it be attached to the sentence after it.
The structure looked fragile. After Jill climbed, Jack climbed as well.
If there is no independent clause around the fragment that fits with that fragment’s meaning, then one can be created.
After Jill climbed.→ After Jill climbed, she fell.
Finally, if the fragment is a dependent clause, it can be made into an independent clause by removing the dependent word.
After Jill climbed.→ Jill climbed.
Two independent clauses separated by only a comma is a comma splice. There are a number of ways to fix a comma splice. One of these ways is to add a coordinating conjunction after the comma when it makes sense to do so. There are seven coordinating conjunctions: and, or, but, so, for, yet, and nor.
Jack climbed, Jill did not. → Jack climbed, but Jill did not.
Alternatively, an end punctuation or semi-colon may replace the comma.
Jack climbed, Jill did not. → Jack climbed; Jill did not.
Finally, a dependent word may be added to one of the independent clauses to make it a dependent clause.
Jack climbed, Jill did not. → While Jack climbed, Jill did not.
A run-on is a sentence crime that is similar to a comma splice except that nothing at all separates the two independent clauses. Fixing a run-on is very similar to fixing a comma splice. An end punctuation, semi-colon, or comma with coordinating conjunction may be used to separate the two independent clauses.
Jack climbed Jill did not. → Jack climbed. Jill did not.
A dependent word may be added to one of the dependent clauses if doing so makes sense.
Jack climbed Jill did not. → Jack climbed while Jill did not.
* Portions of this handout are adapted from Rita Smilkstein’s Tools for Writing (Orlando: Harcourt, 1998), which serves as the foundation for English 097 at Skagit Valley College (MVC).