TOEIC Link Writing: Comma Splice and Run-On Sentence Repair

On the TOEIC Link Writing module, a single recurring error can quietly hold your score below the band you are capable of: joining two complete sentences the wrong way. Under time pressure, writers reach for a comma when the grammar requires something stronger, and the result is a comma splice or a run-on. Raters notice these instantly because they signal weak control of clause boundaries — one of the mechanics dimensions the scoring rubric explicitly weighs.

The good news is that this is a closed problem. Unlike vocabulary range, which you widen slowly over months, clause-boundary repair is a small set of moves you can learn in an afternoon and apply automatically. This article gives you the five repair options, a fast way to detect the error while drafting, and the judgment to pick the right fix for the meaning you want.

What Counts as a Comma Splice or a Run-On

Both errors come from the same root cause: two independent clauses (each a complete sentence that could stand alone) stuck together without the right connector.

• A comma splice joins them with only a comma: The report was late, the client was frustrated.
• A run-on (or fused sentence) joins them with nothing at all: The report was late the client was frustrated.

The test is simple. Cover everything after the comma. Is what remains a complete sentence? Now cover everything before it. Complete sentence again? If both halves stand alone, a comma is not enough to hold them together. This two-step check takes two seconds and catches nearly every instance while you are still drafting.

Note what is not an error. If one half cannot stand alone — Because the report was late, the client was frustrated — you have a dependent clause plus an independent one, and the comma is correct. The whole problem lives in the boundary between two independent clauses.

The Five Repair Moves

When you find two independent clauses fused or spliced, you have five clean ways to fix them. Each carries a slightly different meaning, so the choice is not arbitrary.

1. Split into two sentences (period). The report was late. The client was frustrated. The safest move. It always works and never introduces a new error. Use it when the two ideas are simply sequential and you want no risk. The cost is a slightly choppier rhythm if you overuse it.

2. Coordinating conjunction with a comma (, and / , but / , so). The report was late, so the client was frustrated. Use this when you want to name the relationship — cause, contrast, addition. The comma stays, but now it is doing legitimate work because the conjunction carries the join. This is the most common fix in business writing because it shows the logical link.

3. Semicolon. The report was late; the client was frustrated. Use when the two ideas are closely related and you want them balanced without spelling out the connection. The semicolon signals a tighter bond than a period. Powerful, but use sparingly — one or two per response is plenty, and overuse reads as showing off.

4. Semicolon plus a conjunctive adverb. The report was late; therefore, the client was frustrated. This is the higher-register version of move 2. The pattern is strict: semicolon, then the adverb (however, therefore, consequently, moreover), then a comma. Getting this pattern exactly right earns credit; getting it wrong (a comma before however joining two clauses) is itself a comma splice, so deploy it only when confident.

5. Subordinate one clause. Because the report was late, the client was frustrated. Turn one independent clause into a dependent one with a subordinator (because, although, when, since, while). This is often the strongest choice because it shows the relationship between ideas and demonstrates syntactic range — exactly what pushes a response into the higher bands.

Choosing the Right Repair for the Meaning

The five moves are not interchangeable. Raters reward writers who pick the join that matches the logic:

• Pure sequence, equal weight → period or semicolon.
• Explicit cause or contrast → coordinating conjunction (move 2) or conjunctive adverb (move 4).
• One idea clearly supports or explains the other → subordination (move 5), so the main clause carries the main point.

A quick worked example. You want to express that a delay caused a complaint. A comma splice — Shipping was delayed, several customers complained — can become any of these:

• Shipping was delayed, so several customers complained. (names the cause plainly)
• Because shipping was delayed, several customers complained. (foregrounds the complaint as the main point)
• Shipping was delayed; consequently, several customers complained. (formal register)

All three are correct. The one you choose depends on which idea you want in the spotlight — and that judgment is what a high-scoring writer demonstrates. This choice is closely tied to controlling emphasis and focus, which we cover in TOEIC Link Writing: Emphasis and Focus Control, and to selecting the right connector, covered in TOEIC Link Writing: Transition Signal Precision and Conjunctive Adverb Selection.

Spotting the Error Fast Under Time Pressure

You will not have time to diagram sentences during the test. Build these habits instead:

1. Watch every comma that follows a complete thought. The moment you type a comma, glance back. If the words before it already form a full sentence, ask whether the words after it do too. If yes, you need one of the five repairs.
2. Distrust long sentences with no conjunction or period. Run-ons hide in ambitious sentences. If a sentence has run past fifteen or twenty words with no and, but, because, or period, stop and check the boundaries.
3. Beware the transition-word trap. Words like however, therefore, and for example feel like conjunctions but are adverbs. The plan was solid, however the budget was tight is a comma splice. It needs a semicolon or a period before however.

Why This One Fix Moves Your Score

Mechanics accuracy is a scored dimension on TOEIC Link Writing, and comma splices are among the most visible mechanics errors an English rater sees. Two or three of them in a short response create an impression of shaky control that even strong vocabulary cannot fully offset. Conversely, a response that joins clauses correctly — and occasionally uses subordination or a well-placed semicolon — reads as controlled and mature.

Because the repair set is small and fixed, this is one of the highest-return areas to drill before your test. Master the two-second boundary check and the five moves, and you close off an entire category of error that would otherwise leak points on every response.

For the broader picture of how mechanics fits into the full scoring model, see TOEIC Link Writing: Task Types and Scoring Criteria, and to keep your revision pass efficient, TOEIC Link Writing: Self-Editing and Revision Protocol Under Time Constraint.

Quick Reference

• Comma splice = two full sentences joined by only a comma. Run-on = joined by nothing.
• Detect it: after any comma, check whether both sides could stand alone.
• Fix it five ways: period · comma + conjunction · semicolon · semicolon + conjunctive adverb · subordination.
• Choose by meaning: subordinate to show relationship and range; split or use a semicolon for equal-weight ideas.
• Trap: however / therefore are adverbs, not conjunctions — they need a semicolon, not a comma.

Drill the two-second check on every practice response until it becomes automatic. Clause-boundary control is a small skill with an outsized effect on how controlled your writing feels — and on the score it earns.