Definition · Plain-language
Run-on sentence
A run-on sentence occurs when two or more independent clauses are joined without the correct punctuation or coordinating conjunction needed to separate them.
The step most authors miss
Doing CRediT right? Don’t stop at the statement.
A CRediT statement credits you inside one paper. The recognition CRediT was built for happens when those roles are tied to you, persistently. Sign in with your ORCID — free — and claim your CRediT contributions on casrai.org, the home of the standard. They become a verified, portable part of your identity, not a line that disappears into one PDF.
Free: claim your contributions, then export a journal-ready CRediT statement, schema.org structured data, JATS XML, CSV or BibTeX — and preview your public profile. A membership publishes that profile publicly and verifies the journals you serve.
What a run-on sentence is
A run-on sentence combines two or more independent clauses without the punctuation or conjunction needed to show where one ends and the next begins. The term covers two distinct errors. A fused sentence has no punctuation between the clauses at all: "The experiment ran for six weeks the results were inconclusive." A comma splice uses a comma alone — without a coordinating conjunction — between two independent clauses: "The experiment ran for six weeks, the results were inconclusive." A comma is not strong enough to join two independent clauses on its own; it needs a conjunction (and, but, so) beside it, or it should be replaced by a semicolon or a full stop. Both errors signal to readers — and editors — that the writer has not controlled clause boundaries.
Four ways to fix a run-on sentence
Fix 1 — Full stop: Split the run-on into two separate sentences. "The experiment ran for six weeks. The results were inconclusive." This is the simplest fix and works when the ideas are distinct. Fix 2 — Semicolon: Join the two clauses with a semicolon if they are closely related. "The experiment ran for six weeks; the results were inconclusive." Fix 3 — Comma plus coordinating conjunction: Add a comma and a FANBOYS conjunction. "The experiment ran for six weeks, but the results were inconclusive." The conjunction clarifies the logical relationship. Fix 4 — Subordinating conjunction: Restructure one clause as a dependent clause. "Although the experiment ran for six weeks, the results were inconclusive." This fix also lets you signal which idea is primary.
Common run-ons and how to spot them
Run-ons often arise when writers follow a train of thought without pausing to mark clause boundaries, or when they know a comma indicates a pause and use it without checking whether it is strong enough. Transitional adverbs — however, therefore, moreover, consequently, nevertheless — are frequent culprits: placing a comma before them between two independent clauses creates a comma splice. "The data was clear, however the committee delayed." The fix is a semicolon before the adverb and a comma after: "The data was clear; however, the committee delayed." Reading aloud helps catch run-ons: if you reach what feels like the end of a sentence but the text continues without pause, check whether a clause boundary has been left unmarked.
Key facts
At a glance
- Definition: two or more independent clauses joined without correct punctuation or conjunction
- Fused sentence: no punctuation between clauses at all
- Comma splice: a comma alone between two independent clauses, without a conjunction
- Fix 1: full stop — split into two sentences
- Fix 2: semicolon — join closely related clauses
- Fix 3: comma + coordinating conjunction (FANBOYS)
- Fix 4: subordinating conjunction — restructure one clause as dependent
- Adverb trap: however, therefore etc. after a comma create a comma splice; use a semicolon before them
Common misconceptions
What people often get wrong
Often heard: A comma always indicates a sufficient pause between two ideas.
Actually: A comma is not strong enough to join two independent clauses on its own. Using only a comma between two clauses is a comma splice, one of the two types of run-on sentence. A semicolon, a full stop, or a comma-plus-conjunction is needed.
Often heard: Run-on sentences are always very long.
Actually: A run-on can be short: "She left he stayed." is a fused sentence despite having only four words. Length is irrelevant — the error is the missing boundary between two independent clauses, regardless of how many words each clause contains.
Often heard: Words like "however" and "therefore" can join two independent clauses after a comma.
Actually: However, therefore, moreover and similar conjunctive adverbs are adverbs, not conjunctions. They cannot join independent clauses after only a comma. The correct punctuation is a semicolon before and a comma after: "The study was large; however, the dropout rate was high."
Common questions
FAQ
What is a run-on sentence?+
A run-on sentence incorrectly joins two independent clauses without the punctuation or conjunction needed to mark the boundary between them. A fused sentence has no mark at all; a comma splice uses a comma without a conjunction. Both make sentences harder to read and signal a loss of grammatical control. The fix is to separate, conjoin or subordinate the clauses correctly.
What is a comma splice?+
A comma splice is one type of run-on sentence in which two independent clauses are joined by a comma alone, without a coordinating conjunction. Example: "The report was late, the editor was frustrated." Fix options: add a coordinating conjunction ("but the editor"), replace the comma with a semicolon, split into two sentences, or restructure with a subordinating conjunction.
How do I fix a run-on sentence?+
There are four main fixes: (1) add a full stop and start a new sentence; (2) replace the junction with a semicolon if the clauses are closely related; (3) add a comma plus a coordinating conjunction (for, and, nor, but, or, yet, so); (4) make one clause dependent using a subordinating conjunction (because, although, since, when). Choose the fix that best reflects the logical relationship between the ideas.
Going deeper
