Difficulty: Beginner | Prerequisites: None, though familiarity with basic sentence structure (subjects and verbs) is helpful.
This topic sits at the foundation of college-level writing. Every essay, research paper and discussion post you submit in ENGL 101 (and beyond) will be marked down for run-ons, comma splices and fragments. These are the three most common sentence-boundary errors, and professors flag them constantly. If you can spot and fix these, your writing immediately reads as more polished and controlled.
The material here is drawn from the ENGL 101 Grammar Review at Michigan State University and aligns with the strategies in Rules for Writers.
A run-on sentence jams two complete thoughts together without proper punctuation. A comma splice does the same thing but with only a comma holding them apart. A fragment is the opposite problem: a piece of a sentence passed off as if it were whole. Learn to recognise all three, and you have the single fastest way to clean up your academic writing.
Independent clause
A group of words that contains a subject and a verb and expresses a complete thought. It can stand alone as a sentence. In simple terms: if it makes sense on its own, it is an independent clause.
Run-on sentence (fused sentence)
Two or more independent clauses joined with no punctuation or conjunction between them. Think of it as two sentences crammed into one with nothing holding them apart.
Comma splice
Two independent clauses joined by only a comma, without a coordinating conjunction. In simple terms: you stuck a comma where you needed something stronger, like a full stop, a semicolon or a conjunction.
Sentence fragment
A group of words punctuated as a sentence but lacking a subject, a verb or a complete thought. Think of it as a sentence that got cut short, or a dependent clause left stranded on its own.
Coordinating conjunction (FANBOYS)
The seven words that can join two independent clauses when preceded by a comma: for, and, nor, but, or, yet, so. The mnemonic FANBOYS is the standard way to remember them.
Subordinating conjunction
A word that turns an independent clause into a dependent one (because, although, when, if, since, while, after, before, unless, until, etc.). In simple terms: it makes a clause unable to stand alone.
Semicolon
A punctuation mark (;) used to join two closely related independent clauses without a conjunction. Think of it as halfway between a comma and a full stop.
Read the sentence and ask: does this contain two (or more) independent clauses? If it does, check what sits between them.
Nothing at all between the clauses → run-on (fused sentence).
Example: Her car would not start she was late for class.
Only a comma between the clauses → comma splice.
Example: It was raining, Naomi could not find her umbrella.
Any of these strategies will correct a run-on or a comma splice. Choose whichever reads best in context.
Separate into two sentences. Place a full stop between the clauses.
Her car would not start. She was late for class.
Use a comma + coordinating conjunction (FANBOYS). Insert a comma followed by for, and, nor, but, or, yet, or so.
Her car would not start, so she was late for class.
Use a semicolon. Join two closely related clauses with a semicolon.
Her car would not start; she was late for class.
Use a semicolon + conjunctive adverb. Words like however, therefore, consequently, moreover can follow a semicolon (and are themselves followed by a comma).
Her car would not start; therefore, she was late for class.
Subordinate one clause. Turn one independent clause into a dependent clause with a subordinating conjunction (because, since, although, when, etc.).
Because her car would not start, she was late for class.
Every time you revise an essay draft, run a quick scan for spots where two ideas sit side by side with weak or missing punctuation. Fixing these before submission is the single easiest way to raise the quality of your writing in any course.
A fragment is missing one of three things: a subject, a main verb, or a complete thought. The most common type in student writing is a dependent clause punctuated as its own sentence.
Dependent-clause fragment: starts with a subordinating conjunction (because, although, when, if) and is cut off from the independent clause it belongs to.
Example: Because she met him on Instagram. She thought it was a good idea to be cautious.
Phrase fragment: a participial phrase, appositive or prepositional phrase stranded as a sentence.
Example: Her mother making pancakes for dinner in the small apartment.
Afterthought fragment: a trailing detail broken off from the previous sentence, often beginning with especially, such as, including or that.
Example: The dog loved his new toys. Especially the ones that squeaked.
Attach the fragment to the sentence it belongs with. Remove the full stop and, if needed, add a comma.
Because she met him on Instagram, she thought it was a good idea to be cautious.
Rewrite to include the missing element. Add a subject or a main verb so the fragment becomes a complete sentence.
Fragment: Her mother making pancakes for dinner in the small apartment.
Fixed: Maggie remembered her mother making pancakes for dinner in the small apartment. (Fragment folded into the previous sentence.)
Combine with the preceding sentence.
Fragment: The dog loved his new toys. Especially the ones that squeaked.
Fixed: The dog loved his new toys, especially the ones that squeaked.
Fragments occasionally appear intentionally in creative writing and advertising for stylistic effect. In academic and professional writing, they are treated as errors. If your professor marks a fragment, the fix is almost always to attach it to the sentence next to it.
"A long sentence is a run-on." Length has nothing to do with it. A short sentence can be a run-on (I ran she walked) and a long sentence can be perfectly correct if its clauses are joined properly.
"A comma is enough to join two sentences." A comma alone between two independent clauses is a comma splice, not a valid join. You need a comma plus a coordinating conjunction, or a semicolon, or a full stop.
"Fragments are always short." A fragment can be quite long. Although the team had been preparing for months and everyone felt confident about the final presentation is a fragment because it is an entire dependent clause with no independent clause to complete it.
"Starting a sentence with 'because' is always wrong." Starting with because is fine as long as the dependent clause is followed by an independent clause in the same sentence. The error only occurs when the because-clause is left stranded as its own sentence.
⚠️ The homework worksheet asks you to identify and correct each error. Be ready to name the error type (run-on, comma splice or fragment) and supply a corrected version using one of the five strategies.
⚠️ Comma splices are the most commonly tested error on grammar exams because students often think a comma is sufficient between two clauses.
⚠️ Fragments beginning with subordinating conjunctions (because, although, when) appear frequently on exams. The fix is almost always to attach them to the neighbouring independent clause.
⚠️ Expect at least one sentence that could be read two ways depending on where you place the clause boundary (e.g., The parents ate the baby slept in her stroller). These test whether you can find the subject-verb pairs.
Label each sentence as correct (C), a run-on (RO), a comma splice (CS) or a fragment (F).
She finished her essay then she went to bed. ___
Although it was late. ___
The lecture was cancelled; the professor was ill. ___
We left early, the traffic was terrible. ___
Running through the park on a Sunday morning. ___
Answers: 1 = RO, 2 = F, 3 = C, 4 = CS, 5 = F
Each question below is taken from the ENGL 101 Grammar Review worksheet. The error type is identified, then a corrected version is given.
Q: Correct this run-on: "Juan and David recognized each other they had been in the first grade together."
A: Run-on (fused sentence). Two independent clauses with no punctuation between them. Corrected: Juan and David recognized each other; they had been in the first grade together. Alternative: Juan and David recognized each other because they had been in the first grade together.
Q: Correct this run-on: "Her car would not start she was late for class."
A: Run-on (fused sentence). Corrected: Her car would not start, so she was late for class. Alternative: Her car would not start. She was late for class.
Q: Correct this comma splice: "It was raining, Naomi could not find her umbrella."
A: Comma splice. Two independent clauses joined by only a comma. Corrected: It was raining, and Naomi could not find her umbrella. Alternative: It was raining; Naomi could not find her umbrella.
Q: Correct this run-on: "The parents ate the baby slept in her stroller."
A: Run-on (fused sentence). This one is tricky because the clause boundary is hard to see at first. The two clauses are "The parents ate" and "the baby slept in her stroller." Corrected: The parents ate while the baby slept in her stroller. Alternative: The parents ate. The baby slept in her stroller.
Q: Correct this run-on: "Eli wants to quit smoking this habit is too expensive."
A: Run-on (fused sentence). Corrected: Eli wants to quit smoking; this habit is too expensive. Alternative: Eli wants to quit smoking because this habit is too expensive.
Q: Correct this fragment: "The dog loved his new toys. Especially the ones that squeaked."
A: Fragment. "Especially the ones that squeaked" has no subject or verb. Corrected: The dog loved his new toys, especially the ones that squeaked.
Q: Correct this fragment: "Maggie remembered her childhood. Her mother making pancakes for dinner in the small apartment."
A: Fragment. The second sentence is a participial phrase with no main verb ("making" is a participle, not a finite verb). Corrected: Maggie remembered her childhood, her mother making pancakes for dinner in the small apartment. Alternative: Maggie remembered her childhood. Her mother used to make pancakes for dinner in the small apartment.
Q: Correct this fragment: "She decided to meet her new friend in a public place. That they had arranged over e-mail."
A: Fragment. "That they had arranged over e-mail" is a relative clause that belongs with the previous sentence. Corrected: She decided to meet her new friend in a public place that they had arranged over e-mail.
Q: Correct this fragment: "Because she met him on Instagram. She thought it was a good idea to be cautious."
A: Fragment. The first sentence is a dependent clause beginning with "because." Corrected: Because she met him on Instagram, she thought it was a good idea to be cautious.
Q: Correct this fragment: "I cannot wait until President's Day. Finally, a day off."
A: Fragment. "Finally, a day off" has no verb. Corrected: I cannot wait until President's Day, which is finally a day off. Alternative: I cannot wait until President's Day. It will finally be a day off.
This material connects directly to comma rules and punctuation more broadly. Once you can identify independent and dependent clauses, you are better equipped to handle comma usage with introductory elements, compound sentences and nonrestrictive clauses. It also feeds into paragraph-level revision strategies covered later in ENGL 101, where sentence-boundary control is the foundation of clear, readable prose.
Related Terms / Search Tags
run-on sentence, fused sentence, comma splice, sentence fragment, independent clause, dependent clause, subordinate clause, coordinating conjunction, FANBOYS, subordinating conjunction, semicolon, conjunctive adverb, sentence boundary errors, grammar review, ENGL 101, English Composition, Rules for Writers, comma rules, punctuation errors, sentence structure, clause identification, Michigan State University