Run-On Sentences — What They Are & How to Fix Them

A run-on sentence occurs when two or more independent clauses (complete thoughts with a subject and verb) are joined without correct punctuation or an appropriate connecting word. There are two main types: the fused sentence (no punctuation at all: I was hungry I ate) and the comma splice (clauses joined only by a comma: I was hungry, I ate). Both are grammatical errors in formal writing.

A comma splice occurs when two independent clauses are joined with only a comma, without a coordinating conjunction: It was raining, we stayed inside. A comma alone is too weak to join two independent clauses. Commas do join clauses — but only when followed by a coordinating conjunction (and, but, so, yet): It was raining, so we stayed inside. Without the conjunction, use a semicolon or full stop instead.

1) Separate into two sentences with a full stop: She was tired. She went to bed. 2) Use a semicolon between the clauses: She was tired; she went to bed. 3) Add a coordinating conjunction (FANBOYS) with a comma: She was tired, so she went to bed. 4) Use a subordinating conjunction: Because she was tired, she went to bed. Choose the method that best shows the relationship between the ideas.

A comma is correct between two independent clauses ONLY when followed by a coordinating conjunction (for, and, nor, but, or, yet, so — FANBOYS): She worked hard, but she did not succeed. A comma alone between two independent clauses is a comma splice. A comma before a dependent clause at the end of a sentence is generally not needed: She went home because she was tired (no comma before 'because').

In formal academic and professional writing, yes — the comma splice is a grammar error to avoid. However, in literary and creative writing, experienced writers sometimes use comma splices deliberately for effect, pace, or style: I came, I saw, I conquered. The key is intentionality and context. In essays, exam writing, and professional documents, always correct comma splices.

A semicolon joins two closely related independent clauses of equal weight: She studied all night; she was exhausted by morning. A colon introduces an explanation, elaboration or list that follows from the first clause: She had one goal: to pass the exam. Do not use a colon between two equal independent clauses, and do not use a semicolon before a list.

Coordinating conjunctions (FANBOYS: For, And, Nor, But, Or, Yet, So) connect two independent clauses with a comma: He was late, but he apologised. They express different relationships: and (addition), but/yet (contrast), so (result), for (reason), or (alternative), nor (negative alternative). Using FANBOYS with a comma is the most common way to fix a comma splice in everyday writing.

'But' is a coordinating conjunction and joins clauses with a comma: She was tired, but she continued. 'However' is a conjunctive adverb and cannot join two independent clauses with just a comma — it needs a semicolon before it or a new sentence: She was tired; however, she continued. / She was tired. However, she continued. Using 'however' after a comma is a comma splice — a very common error.

Run-on sentences and comma splices directly affect the Grammatical Range and Accuracy score in IELTS and the Language Use criteria in Cambridge exams. Even one run-on sentence signals a lack of control over complex structures. Examiners are specifically trained to notice comma splices. Proofreading for run-ons before submitting your essay is essential.

No. A long sentence with correct punctuation and conjunctions is grammatically fine: Although she had worked all night, she arrived at the office on time and completed the report before the deadline. Length alone does not make a sentence wrong. The issue is only when independent clauses are joined without the appropriate punctuation or connectors. Writing long, correctly punctuated sentences is a mark of advanced English proficiency.