Common Writing Error: Run-on Sentences

Run-on sentences are one of the most common grammar mistakes IELTS test-takers make. They often happen when a candidate has many ideas but tries to write them all in one sentence without using the right punctuation or linking words. This mistake can lower your Grammatical Range and Accuracy score.

1. What is a Run-on Sentence?
A run-on sentence happens when two or more complete sentences are joined without correct punctuation or linking words. In other words, the grammar structure is wrong, even if the ideas are connected.

There are two main types:

1. Fused sentence – two sentences with no punctuation at all.
   ❌ The government should invest more in renewable energy this will reduce pollution.
   → Two sentences are “fused” together with nothing in between.
2. Comma splice – two sentences joined only by a comma.
   ❌ Many people prefer online shopping, it is more convenient.
   → The comma is not enough; you need a linking word or different punctuation.

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2. Examples from IELTS Writing

Task 1 – Academic
❌ The percentage of commuters using trains increased steadily it reached 60% in 2019.
✔ The percentage of commuters using trains increased steadily, and it reached 60% in 2019.
✔ The percentage of commuters using trains increased steadily; it reached 60% in 2019.
✔ The percentage of commuters using trains increased steadily. It reached 60% in 2019.

Task 1 – General Training (letter)
❌ I am writing to ask for a replacement my toaster stopped working yesterday.
✔ I am writing to ask for a replacement because my toaster stopped working yesterday.
✔ I am writing to ask for a replacement. My toaster stopped working yesterday.

Task 2 – Academic or General Training
❌ Some people believe university education should be free tuition fees are too expensive for many families.
✔ Some people believe university education should be free because tuition fees are too expensive for many families.
✔ Some people believe university education should be free. Tuition fees are too expensive for many families.

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3. Basic Punctuation Rules to Avoid Run-ons
Here are four reliable ways to fix a run-on sentence:

Rule 1: Use a period or a full stop (.) 
Separate the ideas into two sentences.
The city has built more bike lanes. As a result, traffic congestion has decreased.

Rule 2: Use a comma + a coordinating conjunction (FANBOYS)
FANBOYS = for, and, nor, but, or, yet, so
The number of international students has increased, and many universities have expanded their programs.

Rule 3: Use a semicolon (;)
Join closely related ideas without a linking word.
The population grew rapidly; housing supply could not keep up.
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Rule 4: Use a subordinating conjunction
​Make one clause dependent on the other. Common subordinating conjunctions: because, although, while, since, when, if, etc.
Although the cost of living is high, many people choose to move to the city for better job opportunities.

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4. Why This Matters for IELTS
Run-on sentences make your writing harder to follow and can lead to lower Grammar scores. In IELTS Writing, clear sentence boundaries are important for:

• Task Response – Ideas are easier to understand when separated clearly.
• Coherence and Cohesion – Logical links between sentences are shown with correct connectors.
• Grammatical Range and Accuracy – Accurate punctuation is part of grammar.

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5. Quick Self-Check
After writing a sentence, ask:

1. Does it contain two complete sentences?
2. If yes, have I used correct punctuation or a linking word to join them?
3. If not, fix it using one of the four rules above.

In short: In IELTS, it’s better to write two clear, short sentences than one long run-on. Clear structure shows control of grammar and improves your score.