Run-on Sentence and Its Two Types: Comma-splice and Fused Sentence

In this post, we’ll cover what are run-on sentences and, more importantly, how to fix them.

What is a run-on sentence?

If you join two sentences just by a comma or by nothing, you get a run-on sentence, which is an error. (Sentences can’t be joined like this.) In a run-on sentence, two sentences essentially run into each other and cause an error, just like two vehicles run into each other and cause an accident. Examples:

The police remained tight-lipped, they said investigations were on. [Two sentences joined by a comma]

The police remained tight-lipped they said investigations were on. [Two sentences joined by nothing]

Run-on sentences result when students graduate from expressing one idea per sentence to multiple ideas per sentence but without knowing the tools to accomplish it, calling for teaching interventions such as compound and complex sentences. Run-on sentences are often an indication of growing syntactic maturity in students’ writing, like stumbling is an indication of growing maturity in toddlers’ walking. Some, however, stumble far too long for want of appropriate tools.

Comma splice vs. fused sentence

Run-on sentences are of two types, comma-splice and fused sentence, with the comma-splice being much more common.

A comma-splice results when two sentences are joined by just a comma. The first sentence we saw earlier is an example of comma splice.

The police remained tight-lipped, they said investigations were on. [Comma-splice]

A fused sentence results when two sentences are joined by nothing. The two sentences are simply placed next to each other. The second sentence we saw earlier is an example of fused sentence.

The police remained tight-lipped they said investigations were on. [Fused sentence]

In comma splice, the person clearly knows the boundary between the two sentences, or else he wouldn’t use a comma. It’s another matter that comma is not the appropriate way to separate two sentences.

In fused sentences though, the person either knows the boundary and missed it in haste or doesn’t know the boundary between the two sentences, implying he faces difficulty in recognizing the second sentence.

More resources on run-on sentences:

How to fix run-on sentences?

The fundamental to fixing run-on sentences is, first, to identify two sentences and, second, to join them correctly.

1. How to identify two sentences?

This holds only for fused sentences as people know sentence boundary (where the first sentence ends and the second starts) in case of comma splice. Once we identify the sentence boundary, we can treat fused sentences and comma splices at par and join them the correct way.

1.1 If you missed the sentence boundary in haste

You know where the first sentence ends and the second starts, but you missed it in haste, resulting in a fused sentence. The simplest way to identify sentence boundary in such cases is to read what you’ve written loudly. You’ll likely take a pause at the boundary and notice the break between two complete thoughts. Your voice too will likely drop at the boundary.

1.2 If you can’t recognize the second sentence as a sentence

This is a serious problem, and you need to go back to basics of sentences. Learn the four types of simple sentences containing one independent clause: declarative, interrogative, imperative, and exclamatory. Also learn the three types of sentences containing multiple clauses: compound, complex, and compound-complex sentences. The second sentence, after all, need not be a simple sentence.

Besides learning different types of sentences, be aware that the second sentence may be elliptical (repeated words may be omitted) but has to treated as a sentence. Example:

He won six medals at the event, his teammate just one. [Comma splice. Second sentence is elliptical]

2. How to join two sentences?

Once you recognize the two sentences, correcting run-on sentences – whether comma splice or fused sentence – is all about learning few rules. Here are five ways, of which one or more may come handy in any case of run-on.

2.1 Write two sentences

The easiest way to correct run-on sentences is to simply write them as separate sentences.

People gathered around the accident victim, no one came forward to help. [Comma splice]

People gathered around the accident victim. No one came forward to help. [Correct]

She will stand by me, after all she is my friend. [Comma splice]

She will stand by me. After all, she is my friend. [Correct. After all is an introductory phrase starting the second sentence.]

However, this is sometimes not a desirable option because, with this method, you create two simplistic sentences, which defeats the purpose of combining ideas into a longer sentence. It is better to learn how to combine them correctly than to take a step back. In some cases, this method is also not desirable because writing two sentences may strip away the close relationship between them. For instance, in the first example above, joining the two sentences by coordinating conjunction but will also express contrast between the two (covered in 2.3) and hence is better than writing two sentences.

This method can work if you don’t need to express any additional relationship between the two sentences (like in the second example, where the introductory phrase provides transition), and you’re fine with two separate sentences.

In contrast to this method, the next four result in one sentence, and they by and large also express some relationship between the two sentences.

2.2 Separate the two sentences by a semicolon

You can join two closely related sentences with a semicolon.

It’s an ideal way to join two sentences when the second sentence contains a conjunctive adverb (however, therefore, thus, now, otherwise, next, and so on), which builds logical connection between the two sentences. Because of this connection, such sentences are closely related and automatically qualify the criterion for use of semicolon.

Like in life, few things are black or white, the havoc caused to the planet by us is also not in black or white it is in shades of grey. [Comma splice/ Fused sentence. It contains both the errors.]

Like in life, few things are black or white. The havoc caused to the planet by us is also not in black or white; it is in shades of grey. [Correct]

Several infrastructure projects have been launched in the city, however nothing much seems to have changed here. [Comma splice. Conjunctive adverb however signals close relation between the two sentences. More on this later in the post]

Several infrastructure projects have been launched in the city; however, nothing much seems to have changed here. [Correct]

This method has limited use though because the two sentences should be closely related.

2.3 Join the two sentences by a coordinating conjunction

You can join two sentences by a comma and a coordinating conjunction (FANBOYS).

People gathered around the accident victim, no one came forward to help. [Comma splice]

People gathered around the accident victim, but no one came forward to help. [Correct]

Climate politics has shifted in the last few years, that gives us hope. [Comma splice]

Climate politics has shifted in the last few years, and that gives us hope. [Correct]

Do these sentences ring a bell? They’re compound sentences.

The seven coordinating conjunctions can express few types of relationships between the two sentences, a case in point being but, which expresses relationship of contrast in the first example.

You can’t use this method though if the relationship between the two sentences isn’t covered by the seven coordinating conjunctions. This, for example, can’t be corrected by FANBOYS.

Working as a designer is not easy, a designer has to regularly come up with new ideas to capture consumers’ imagination. [Comma splice]

2.4 Convert one of the sentences into a dependent clause

You can convert one of the sentences into a dependent clause and join it to the other sentence. Examples:

It serves an important reminder to our educational institutions, there majority of graduates are churned out without marketable skills. [Comma splice]

It serves an important reminder to our educational institutions, where majority of graduates are churned out without marketable skills. [Correct. The second sentence has been converted into a dependent clause (relative clause)]

Working as a designer is not easy, a designer has to regularly come up with new ideas to capture consumers’ imagination. [Comma splice]

Working as a designer is not easy because a designer has to regularly come up with new ideas to capture consumers’ imagination. [Correct. The second sentence has been converted into a dependent clause (adverb clause)]

Whether you use coordinating conjunction (2.3) or subordinating conjunction (2.4) mainly depends on what relationship exists between the two sentences.

2.5 Convert one of the sentences into a phrase

You can occasionally convert one of the sentences into a phrase and join it to the other sentence. Examples:

The police remained tight-lipped they said investigations were on. [Fused sentence]

The police remained tight-lipped, saying investigations were on. [Correct. The second sentence has been converted into a phrase (participial phrase)]

Several vaccines have now been developed for Covid-19, it’s a deadly virus. [Comma splice]

Several vaccines have now been developed for Covid-19, a deadly virus. [Correct. Appositive phrase]

If you noticed, in the last two methods, a dependent clause or a phrase can be joined to a sentence by a comma or nothing. But a sentence can’t be joined to another the same way as it would result in run-on.

Four common run-on errors

Here are four common run-on errors, with the first two being more common than the last two. Each pattern has been explained through few examples, but you may find many more examples in the resource on examples linked earlier.

1. Conjunctive adverb and introductory phrase used like coordinating conjunction

One of the most common reasons for run-on sentences is using conjunctive adverbs and introductory phrases like we use coordinating conjunctions.

1A. Conjunctive adverbs

Some use conjunctive adverbs (also called transition words in common parlance) such as therefore, however, hence, and now like we use coordinating conjunctions (FANBOYS). Examples:

We missed the bus, now we’ll have to go by road. [Comma splice]

If you’ve too many friends, you can’t find time to build deeper bonds with most of them, therefore, have few but good friends. [Comma splice. Sometimes two commas are used around the conjunctive adverb]

Both are comma splice errors because the underlined parts are complete sentences. In the above sentences, now and therefore are not coordinating conjunctions – although they too function somewhat similarly – and hence can’t be used and punctuated like them. The best way to avoid mixing the two is to remember common conjunctive adverbs.

How do you correct the error?

Separate them into two sentences (2.1).

We missed the bus. Now, we’ll have to go by road.

If you’ve too many friends, you can’t find time to build deeper bonds with most of them. Therefore, have few but good friends.

Alternatively, if you want to write one sentence, you can use a semicolon because, as we saw earlier, a conjunctive adverb denotes close relationship between two sentences (2.2).

We missed the bus; now, we’ll have to go by road.

If you’ve too many friends, you can’t find time to build deeper bonds with most of them; therefore, have few but good friends.

If you don’t want to use 2.1 or 2.2, you’ll have to drop conjunctive adverbs.

We missed the bus, forcing us to go by road. [Converting second sentence into a phrase (2.5)]

If you’ve too many friends, you can’t find time to build deeper bonds with most of them, so have few but good friends. [Joining with a coordinating conjunction (2.3)]

Here is a little challenging example from a news daily.

The man claimed that he informed the woman that he was married, however, at her instance, he met her at a hotel where he was staying and alleged that since February 2018, she started asking money from him. Source [Comma splice]

The man claimed that he informed the woman that he was married. However, at her instance, he met her at a hotel where he was staying and alleged that since February 2018, she started asking money from him. [Correct]

1B. Introductory phrase

Some introductory phrases, especially those signaling transition, are used like coordinating conjunctions. Examples:

If we’re happy with existing state of affairs, we wouldn’t make the effort to improve things, that’s why, discontent with the existing order is the first step towards innovating new products or services. [Comma splice. Two commas are not uncommon, with the second trying to demarcate the introductory phrase]

The only viable direction to sleep was perpendicular to the mountain wall, in the other direction, we could roll down because of the slope.

If I was put in digital marketing, I could have done wonders for the organization, after all a man is a lion in his own cause.

How do you correct the error?

Separate them into two sentences (2.1). Here is one of the corrections.

If I was put in digital marketing, I could have done wonders for the organization. After all, a man is a lion in his own cause.

Though less preferred, you can use coordinating conjunction (2.3) if it serves the intended meaning.

The only viable direction to sleep was perpendicular to the mountain wall, and in the other direction, we could roll down because of the slope.

2. Second sentence starting with a pronoun

Second sentences starting with a pronoun are prone to run-on error. A case in point is the first example, from the statement of CEO of SII, world’s largest manufacturer of vaccines. Examples:

First of all, vaccine manufacturing is a specialized process, it is therefore not possible to ramp up production overnight. [Comma splice]

My name is Susan, I am a sophomore in Art & Design school. [Comma splice]

Actions and decisions taken in moments of anger aren’t the best, they can bring great misery. [Comma splice]

How do you correct the error?

Any of the five methods we saw earlier can work here. The first, for example, can be corrected in four ways.

First of all, vaccine manufacturing is a specialized process. It is therefore not possible to ramp up production overnight. [Two sentences (2.1)]

First of all, vaccine manufacturing is a specialized process; it is therefore not possible to ramp up production overnight. [Semicolon (2.2). The presence of conjunctive adverb therefore indicates close relationship between the two sentences]

First of all, because vaccine manufacturing is a specialized process, it is not possible to ramp up production overnight. [Converting one into a dependent clause (2.4)]

First of all, vaccine manufacturing is a specialized process, making it difficult to ramp up production overnight. [Converting one into a phrase (2.5)]

3. Second sentence starting with a noun clause or second sentence being an interrogative sentence

Second sentences starting with a noun clause or interrogative sentences as second sentences are prone to run-on error.

Result matters for sure, what matters more is whether we gave our best. [Comma splice. Second sentence starts with a noun clause]

It was a breathtakingly tight contest, how I won has lot to do with luck. [Comma splice. Second sentence starts with a noun clause]

Typing faster would make life easy, don’t you agree? [Comma splice. Second sentence is an interrogative sentence]

How do you correct the error?

Writing two sentences is a good option, but other methods too can work.

4. Preposition used like subordinating conjunction

With an adverb clause following an independent clause, this is a fine sentence.

I started climbing the 8,000-meter peak on May 18 before I was even ready for it.

But these are fused sentences because the underlined parts are sentences, and not dependent clauses. The presence of pronoun that makes the difference.

I started climbing the 8,000-meter peak on May 18 before that I was chilling out on a leisure trip. [Fused sentence]

Happiness increases with money but only till basic needs are met after that money matters much less. [Fused sentence]

How do you correct the error?

Separate them into two sentences (2.1).

I started climbing the 8,000-meter peak on May 18. Before that, I was chilling out on a leisure trip.

Happiness increases with money but only till basic needs are met. After that, money matters much less.

Before that and After that are introductory prepositional phrases, much like in After 10 PM, you’ll hardly see any vehicles on the street.

The two sentences in run-ons may not always be simple

To keep it simple, so far, we looked at run-on sentences containing mostly two simple sentences, those with one independent clause, but the two sentences may not always be simple. The fundamentals though remain the same: Identify two sentences and join them correctly. Examples:

1. I used to commit silly mistakes in mathematics, for which I got feedback from my teacher, after that number of such mistakes has gone down. [Simple sentence (underlined) joined to a complex sentence by a comma, resulting in comma splice]

I used to commit silly mistakes in mathematics, for which I got feedback from my teacher. After that, number of such mistakes has gone down. [Correct]

2. Plants need sunshine and water to grow, but interest doesn’t need any favourable conditions to grow, it only needs debt. [Simple sentence (underlined) joined to a compound sentence by a comma, resulting in comma splice]

Plants need sunshine and water to grow, but interest doesn’t need any favourable conditions to grow. It only needs debt. [Correct]

3. Chasing wealth is a never-ending game it rarely stops at a particular level, and the chasers don’t have enough time and peace of mind to enjoy what they’ve accumulated. [A compound-complex sentence joined to a simple sentence (underlined) by nothing, resulting in a fused sentence]

Chasing wealth is a never-ending game. It rarely stops at a particular level, and the chasers don’t have enough time and peace of mind to enjoy what they’ve accumulated. [Correct]

That’s why earlier in the post (1.2), it was recommended to learn not just the four types of simple sentences but also compound, complex, and compound-complex sentences.

When to use comma splice? [4 scenarios]

Although both fragments and comma splices are scoffed at by grammar police, fragments enjoy more acceptability than comma splices, but comma splices aren’t always bad (fused sentences always are).

Irene Teoh Brosnahan, in her article A Few Good Words for the Comma Splice which was published in 1976 but is still relevant, proposed following conditions under which comma splice can be effective:

  1. Sentences are short and usually parallel in structure.
  2. Relationship between the sentences is paraphrase, repetition, amplification, opposition, addition, or summary.
  3. The text is being used in general or informal English.
  4. Sentences are meant to create rapid movement and/or emphasis.

Something similar is echoed by William Strunk Jr. in The Elements of Style Workbook, “A comma is preferable [over semicolon] when the clauses are very short and alike in form, or when the tone of the sentence is easy and conversational.”

Assuming we’re not writing formally (point #3), here are few valid usages of comma splice, categorized as per relationships mentioned in #2, that fulfil above conditions.

Opposition

A book can be fun to read, a book can be boring as well.

Our product was good before, it’s great now.

Premium service is $99 per month, basic is free.

My fellow Americans, ask not what your country can do for you, ask what you can do for your country. John F. Kennedy

Addition

Flowers waved, bees buzzed, cows grazed.

Medicine didn’t work, therapy didn’t work, exercise did.

With high fever and weakness, I can’t eat, I can’t sleep. [After the introductory phrase, the main clause is parallel to the next sentence.]

Repetition

The days was bad, the day was unbelievably bad.

Summary

The tax raise doesn’t make economic sense, it doesn’t make political sense, it doesn’t make any sense. [The third sentence summarizes the first two.]

Comma splice in such cases not just pass but sail, at least rhetorically. There are reasons why professional writers use them. However, know your audience before using comma splice in your writing, lest it be taken as an error.

You may also avoid comma splice even if all conditions are met to avoid making the sentence messy. This sentence, for example, will be confusing with too many commas if semicolon is replaced by comma.

In times of prosperity, you’ll be surrounded by friends; in times of adversity, you’ll have to search for them.

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