Run-On Sentences — Grammar Rules & Examples

What are Run-On Sentences?

A run-on happens when independent clauses are merged without a proper connector. There are two types: the fused sentence, where two clauses are jammed together with no punctuation at all, and the comma splice, where a comma alone connects two independent clauses. Both are errors in formal written English.

Run-ons are often caused by two closely related ideas that feel like one continuous thought. The writer is so focused on the content that they forget each independent clause needs its own structural boundary. The fix is not to separate the ideas — it is to show their connection through the right punctuation or conjunction.

At B2 level, a single run-on does not necessarily collapse a piece of writing, but a pattern of run-ons signals that the writer lacks control of sentence boundaries — a core criterion in both IELTS Task 2 and Cambridge advanced writing papers.

Two Types of Run-On Sentences

Every independent clause can stand alone as a sentence. When two are joined, they need either a coordinating conjunction with a comma, a semicolon, a semicolon + conjunctive adverb, or they must be written as separate sentences.

Formula[Independent Clause] + [Independent Clause] without correct connection = run-on

Type 1 — Fused Sentence (no punctuation)

Run-on	Problem	Corrected
The lab results were ready no one had read them yet.	Two independent clauses with no separator.	The lab results were ready, but no one had read them yet.
She applied for the grant she was offered a position instead.	Two separate ideas fused together.	She applied for the grant; she was offered a position instead.

Type 2 — Comma Splice (comma only)

Run-on	Problem	Corrected
The presentation was convincing, the board remained sceptical.	Comma alone between two independent clauses.	The presentation was convincing; however, the board remained sceptical.
He sent the email, she never replied.	Two clauses, comma only — not enough.	He sent the email, but she never replied.

Five Ways to Fix a Run-On

Fix 1 — Use a full stop (period)

The simplest fix. If the two independent clauses express genuinely separate ideas, make them two separate sentences. This is the clearest solution and never produces a new error.

Run-on: The audit was completed the findings were sent to the board.
Fixed: The audit was completed. The findings were sent to the board.
Run-on: She was exhausted, she refused to stop working.
Fixed: She was exhausted. She refused to stop working.

Tip: Two short separate sentences can feel choppy — consider whether the relationship would benefit from an explicit connector. 'She was exhausted, but she refused to stop working' expresses the contrast more clearly.

Fix 2 — Add a coordinating conjunction

Join the two independent clauses with a comma + coordinating conjunction (for, and, nor, but, or, yet, so — FANBOYS). This fix expresses the relationship: contrast (but), addition (and), result (so), alternative (or).

Run-on: The deadline was extended, the quality did not improve.
Fixed: The deadline was extended, but the quality did not improve.
Run-on: She finished the draft she sent it for review.
Fixed: She finished the draft, and she sent it for review.
Run-on: The server was down, we lost two hours of work.
Fixed: The server was down, so we lost two hours of work.

Tip: The coordinating conjunction must be preceded by a comma and must accurately reflect the relationship: 'but' for contrast, 'so' for result, 'and' for addition. Do not use 'so' for every run-on — it makes writing monotonous.

Fix 3 — Use a semicolon

A semicolon joins two independent clauses that are closely related in meaning. It signals 'these two ideas are connected' without specifying how. Use it when the relationship is clear from context or when you want balanced, parallel clauses.

Run-on: The data was missing, the analysis could not proceed.
Fixed: The data was missing; the analysis could not proceed.
Run-on: She presented the findings the panel asked several questions.
Fixed: She presented the findings; the panel asked several questions.

Tip: A semicolon is not a stronger comma — it is an independent clause connector. Both sides of a semicolon must be independent clauses. Never use a semicolon between a dependent clause and an independent clause.

Fix 4 — Use a semicolon + conjunctive adverb

Conjunctive adverbs (however, therefore, nevertheless, consequently, furthermore, moreover) express logical relationships precisely. They follow a semicolon and are followed by a comma.

Run-on: The proposal was rejected, she revised it and resubmitted.
Fixed: The proposal was rejected; however, she revised it and resubmitted.
Run-on: Costs had risen sharply, the project was still approved.
Fixed: Costs had risen sharply; nevertheless, the project was still approved.

Tip: Conjunctive adverbs are not coordinating conjunctions — they cannot join clauses with a comma alone. 'The data was clear, however the board disagreed' is still a comma splice. Correct: 'The data was clear; however, the board disagreed.'

Fix 5 — Use subordination

Turn one independent clause into a dependent clause by adding a subordinating conjunction. This not only fixes the run-on but also makes the relationship between clauses structurally explicit — ideal for academic writing.

Run-on: The sample was too small, the results were unreliable.
Fixed: Because the sample was too small, the results were unreliable.
Run-on: She had no formal training, she outperformed the specialists.
Fixed: Although she had no formal training, she outperformed the specialists.

Tip: Subordination is the most sophisticated fix and the one that most visibly raises writing quality. Using a mix of coordination (Fix 2) and subordination (Fix 5) demonstrates the sentence variety that examiners reward.

Run-On Warning Signals

Two subjects in one sentencescan for a second subject-verb pair — if present, check the connection

Comma without a conjunctioncomma alone between two complete thoughts = comma splice

No punctuation between two complete thoughtsfused sentence

However / therefore after a comma'She was tired, however she continued' — use semicolon before 'however'

Long sentence with several clausescount the clauses — each independent clause needs its own boundary

Run-On vs Correct Compound Sentence

A compound sentence joins two independent clauses correctly. A run-on joins them incorrectly. The content is the same — the difference is the connector.

Run-on — comma splice

The contract was signed, the work began immediately.

Comma alone between two independent clauses — incorrect.

Correct compound sentence

The contract was signed, and the work began immediately.

Comma + coordinating conjunction 'and' — correct.

Run-on — conjunctive adverb after comma

The plan was flawed, therefore it was rejected.

'Therefore' is a conjunctive adverb, not a coordinating conjunction — comma alone is not enough.

Correct — semicolon + conjunctive adverb

The plan was flawed; therefore, it was rejected.

Semicolon before the conjunctive adverb, comma after it.

Common Mistakes

Using a comma before 'however', 'therefore', 'moreover'

✗ The training was useful, however the timing was poor.

The training was useful; however, the timing was poor.

'However', 'therefore', 'moreover', 'consequently', and 'furthermore' are conjunctive adverbs — not coordinating conjunctions. They need a semicolon before them and a comma after.

Fusing two closely related independent clauses

✗ The interview went well she was offered the job the same afternoon.

The interview went well, and she was offered the job the same afternoon.

Two complete thoughts with no separator — a fused sentence. Even when ideas are tightly connected, each independent clause needs a proper connector.

Comma splice with a pronoun subject in the second clause

✗ The manager reviewed the proposal, he approved it immediately.

The manager reviewed the proposal, and he approved it immediately.

A new subject ('he') starting a new clause does not authorise a comma alone. Add the coordinating conjunction 'and', use a semicolon, or split into two sentences.

Overusing 'and' or 'so' to chain multiple clauses

✗ The project started well and costs went up and the timeline slipped and the board intervened.

The project started well, but costs rose and the timeline slipped, so the board intervened.

Chaining independent clauses with repeated 'and' creates a run-on pattern that reads as uncontrolled. Use a variety of connectors — coordinating conjunctions, semicolons, subordination — to show logical structure.

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