Hello.Welcome to the grammar module on sentence boundaries. This module will define errors with boundaries and help you correct common sentence issues such as fused sentences and comma splices.
Let’s begin by reviewing the basic structure of a sentence.
A sentence, very simply is made up of two primary elements: a subject and a verb. The subject of any sentence is the person or thing doing the action of the sentence. The verb is that action. Complete sentences should only have one main subject and one main verb. Being able to identify these elements is the first step to avoiding errors with sentence boundaries.
Let’s look at these errors.
When sentences contain more elements than they should, we call this type of error a sentence boundary error. There are two types we’ll focus on today. Fused sentences and comma splices.
We’ll begin with fused sentences. Sentences that are fused are those that have two independent clauses squished together without any punctuation at all as in this example. Here, there are two complete sentences and no punctuation to separate them.
We can identify this problem by recognizing that there are two subjects and two verbs here. We have incorrectly fused two independent clauses together.
The second type of error is a comma splice. A comma splice is very similar to a fused sentence. We squish together two independent clauses, but this time, we splice the sentence with the incorrect use of a comma. Independent clauses cannot be connected this way.
To correct fused sentences and comma splices, we have four options. We can separate the clauses with a period or a semicolon. Or, we can connect the clauses with a comma and a FANBOYS or a subordinating conjunction. Let’s see how these options work.
Using a period is the simplest way to separate the clauses. Here we’ve just placed a period between the two independent clauses.
You may also use a semicolon to separate the clauses. Most often, semicolons are used just like periods, which means if you can’t put a period there, you can’t use a semicolon either.
To connect the clauses, you can combine them with a comma + a FANBOYS. FANBOYS is an acronym that will help you remember a set of words called coordinating conjunctions. They are for, and, nor, but, or, yet, and so. These words, when used with a comma, can correctly link to independent clauses.
Be careful with FANBOYS! Sometimes we use these words in writing in ways that are not connective. We only need a comma with a FANBOYS when the word is being used to connect two independent clauses. Be careful not to just through a comma before these words every time you see them. You must test whether the clauses that come before and after are independent. If they are, a comma is needed. If one of them is NOT independent, as in these examples, you do not use a comma.
Finally, you can connect the two clauses by making one of them dependent on the other. In a previous module we learned about subordinating conjunctions. These words make a clause dependent. And since dependent clauses must be attached to an independent clause, it’s a good option for correcting a sentence with a boundary error. Here, by adding the word “since” to the first clause, we’ve made it dependent. You can review the most common subordinating conjunctions in your LB Brief.
Now, let’s review. We’ve looked at two primary types errors: fused sentences and comma splices. Both types of errors go beyond the limits of the sentence boundary by incorrectly combining independent clauses. These errors can be corrected in four ways: by using a period, a semicolon, a comma + a FANBOYS, or a subordinating conjunction. Avoiding sentence boundary errors in your writing is imperative to doing well.
Finally, use these additional resources to learn more about clauses or to review as we build on this knowledge in upcoming modules.
Where one sentence ends and another
In a previous module, we learned that a sentence has two parts:
1. A subject
2. A verb
The subject is the person or thing completing the action (always a noun
or pronoun) while the verb is the action being completed.
Being able to identify the subject and the verb of a sentence is how
you will avoid the boundary errors we discuss in this lesson.
The types of errors we’ll learn about in this module are called sentence
boundary errors because they are errors that go beyond the
boundaries of a single sentence. In other words, they contain more
than one subject and verb.
There are two types of errors we’ll cover:
1. Fused Sentences
2. Comma Splices
Fused sentences are those that combine two independent clauses
without any punctuation. They are also called run-on sentences.
I had a ton of homework for math last night I stayed up late to finish it
In this example, two independent clauses – or complete sentences –
are combined incorrectly. We can recognize that by identifying the
subjects and verbs.
More on Fused Sentences
I had a ton of homework for math last night I stayed up late to finish it all.
This example contains two subjects and two verbs:
1. I had
2. I stayed
That means we have two complete sentences.
1. I had a ton of homework for math last night.
2. I stayed up late to finish it all.
Without punctuation, this is a fused sentence. It goes beyond the limits of
Our second sentence boundary error is called a comma splice. Like a
fused sentence, a comma splice contains two independent clauses.
Instead of no punctuation, however, a comma splice error incorrectly
uses a comma to separate the two clauses.
I had a ton of homework for math last night, I stayed up late to finish
Once again, here we have two independent clauses, but this time, the
clauses are “spliced” with a comma. This, too, goes beyond the limits
of sentence boundaries. We cannot connect to independent clauses
with only a comma.
Correcting Boundary Errors
Correcting errors with sentence boundaries is easy. We have four
1. Separate the clauses with a period
2. Separate the clauses with a semicolon
3. Connect the clauses with a comma and a FANBOYS
4. Connect the clauses with a subordinating conjunction
Let’s take a closer look at each of these options.
Separate the Clauses with a Period
This is the simplest option. Separate the clauses by placing a period
I had a ton of homework for math last night. I stayed up late to finish
Separate the Clauses with a Semicolon
In most cases (though not all), a semicolon works just like a period. Many
students have trouble with semicolons, but remembering this rule will help
you use them correctly.
I had a ton of homework for math last night; I stayed up late to finish it all.
Semicolons should be used sparingly. They are most often employed when
there is a clear relationship between the two clauses, such as a comparison
or a contrast.
You can learn more about semicolons in section 40 of your Little, Brown Brief
(pages 322 -326).
FANBOYS is an acronym to help you remember a set of words
called coordinating conjunctions. These words, when
combined with a comma, allow you to connect to
I had a ton of homework for math last night, so I stayed up
late to finish it all.
By adding the comma and the FANBOYS, we have corrected
the sentence boundary error by correctly combining the
sentences. Remember the acronym!
Connect the Clauses with a Comma + a
Warning! You must think carefully when working with FANBOYS. While these
words do function with a comma to connect two independent clauses, that
does NOT mean you will always place a comma before them. Sometimes, these
words are not used in this way.
I bought milk and bread at the store yesterday.
I finished my math homework but not my physics homework.
A FANBOYS only needs a comma before it when the clauses that come before
and after are BOTH independent. Here, the clauses before the FANBOYS are
independent, but the clauses following them are not. Neither contain a subject.
In these cases, no comma is needed. We’ll return to this rule in an upcoming
More on FANBOYS
Connect the Clauses with a Subordinating
In a previous module, you learned that subordinating conjunctions indicate
a dependent clause, which MUST be attached to an independent clause.
The final way to correct a sentence boundary error is to make one of your
clauses dependent on the other.
Since I had a ton of homework for math last night, I stayed up late to
finish it all.
By adding the word “since” to the first clause, we have made this clause
dependent, so it can correctly be connected with the second clause. There
are several subordinating conjunctions. Refer to the module on clauses for a
list or to page 196 of your Little, Brown Brief.
Sentence Boundary Errors
Incorrectly combine two
A fused sentence is one with no
punctuation at all
A comma splices incorrectly
separates the clauses with only a
Separate the clauses with a
Separate the clauses with a
Connect the clauses with a
comma + a FANBOYS
Connect the clauses with a
To learn more about sentence boundary errors:
See section 36 (pages 290 -295) in your Little, Brown Brief
See the Purdue Online Writing Lab resource on clauses. Click here to
visit the page (opens in new window).