Identifying and Correcting Run-On Sentences on the SAT/ACT

  By James Rodkey

(ACT, SAT, SSAT, English Builder, ESOL, and Latin tutor at The Edge Learning Center)

A persistent difficulty for students taking the SAT and ACT arises from the fact that these exams explicitly test fundamentals of English grammar, yet these concepts are rarely explicitly taught in high school English classes. Today we’ll look at one such grammatical concept that is regularly tested on both the ACT and SAT but is at best nebulously understood by most test-takers: run-on sentences.

Read more on the SAT in James’ previous blog “Changes in vocabulary between the old SAT and new SAT format”

english grammar testWhat is a run-on sentence? I ask this question regularly to students, and invariably I receive an answer that sounds something like this: “A run-on is just, like, you know, a sentence that… goes on for too long.” I don’t begrudge students who have this intuition, because most of them have never been formally taught to recognize run-on sentences; moreover, the name is misleading – “run-on” does imply a sentence that just goes on too long. It’s not a particularly helpful or descriptive name for the error.

Length, however, has absolutely nothing to do with run-on sentences. Consider the following two sentences:

Sentence 1

“Amanda likes dogs, Charlotte likes cats.”

Sentence 2

“Daring burglaries by armed men, and highway robberies, took place in the capital itself every night; families were publicly cautioned not to go out of town without removing their furniture to upholsterers’ warehouses for security; the highwayman in the dark was a City tradesman in the light, and, being recognised and challenged by his fellow-tradesman whom he stopped in his character of “the Captain,” gallantly shot him through the head and rode away; the mail was waylaid by seven robbers, and the guard shot three dead, and then got shot dead himself by the other four, “in consequence of the failure of his ammunition:” after which the mail was robbed in peace; that magnificent potentate, the Lord Mayor of London, was made to stand and deliver on Turnham Green, by one highwayman, who despoiled the illustrious creature in sight of all his retinue; prisoners in London gaols fought battles with their turnkeys, and the majesty of the law fired blunderbusses in among them, loaded with rounds of shot and ball; thieves snipped off diamond crosses from the necks of noble lords at Court drawing-rooms; musketeers went into St. Giles’s, to search for contraband goods, and the mob fired on the musketeers, and the musketeers fired on the mob, and nobody thought any of these occurrences much out of the common way.”

The first sentence about Amanda and Charlotte is a run-on. The second sentence, taken from A Tale of Two Cities by Charles Dickens, is not. Let this be the end of any confusion about sentence length pertaining to run-ons.

So, why is the pithy first sentence a run-on while the intimidating, paragraph-length second one is not? The answer is that run-on sentences have problems with how their elements are connected. If we examine the first sentence in terms of its clause structure, we see that it contains two independent clauses (groups of words that are complete sentences on their own):

1.  Amanda likes dogs. (Independent clause)

2. Charlotte likes cats. (Independent clause)

Independent clauses cannot be joined only by a comma in a sentence. Any sentence containing this error is by definition a run-on sentence.

Luckily there are many different ways to fix the Amanda and Charlotte sentence so that it’s no longer a run-on. We could do any of the following things:

  1. Separate the run-on into two complete sentences.

Amanda likes dogs. Charlotte likes cats.

  1. Use a semicolon instead of a comma.

Amanda likes dogs; Charlotte likes cats.

  1. Insert a coordinating conjunction after the comma.

Amanda likes dogs, but Charlotte likes cats.

  1. Make one of the clauses dependent by adding using subordination.

Although Amanda likes dogs, Charlotte likes cats.

Amanda likes dogs whereas Charlotte likes cats.


Now that we know how to recognize and correct run-ons, let’s take a look at how these errors appear on the ACT and SAT. Here’s an example taken from a recent ACT exam:

The first step is to determine whether this sentence is a run-on. Let’s look at the clauses: “The market would open as early as 3:00 a.m. on weekday mornings” is an independent clause (a complete sentence by itself); so is the second part of the sentence – “this is when boat crews would bring their fresh catch to the East River.” Since the two independent clauses are only connected by a comma, this is definitely a run-on sentence. We know that answer choice A must be incorrect; now we need to evaluate B, C, and D to see which one fixes the error.

Both answer choices B and D fail to address the problem; changing “this is when” to “on such mornings” doesn’t prevent the second part of the sentence from being an independent clause, nor does deleting the underlined portion. That leaves us with answer choice C, which is correct because it uses the relative pronoun “which” and creates a dependent (subordinate) clause: “which is when boat crews would bring their fresh catch to the East River” is not a complete sentence, so the sentence is no longer a run-on.

Here’s what a similar question looks like on the SAT, taken from one of the Khan Academy practice exams:

Our first task is the same as it was for the ACT example: determine whether the original sentence is a run-on. Again, let’s look at the clauses. “The couch and chairs, in keeping with the style of the time, are characterized by elegantly curved arms and legs” is a complete sentence, as is the second part – “they are covered in luxurious velvet.” Since these two independent clauses are only separated by a comma, this is also a run-on.

Answer choice A is definitely wrong, so let’s look at B, C, and D to see which one fixes the error. B is still a run-on sentence, and D creates a new problem by deleting the pronoun “they” but leaving the comma – now the sentence has a comma wrongly separating two verbs ( The couch and chairs … are characterized by … , are covered in…). Answer choice C fixes the run-on by deleting both the comma and the pronoun “they” – now the sentence is one clause with two verbs linked by the conjunction “and” with no unnecessary commas.

In these two examples, the original texts contained run-on sentences. Other questions may give a correctly worded sentence with run-ons as incorrect answer choices. In any case, the only way to get these questions consistently correct is to know a run-on when you see it and the various ways to correct it. Learn the rules, and you’ll never miss a run-on sentence question again.

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