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.

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.

 One common grammatical error that learners make, and which stands out in written texts, is forgetting to use past participles after modal verbs combined with the verb "to be." This results in sentences like "should be change" instead of the correct "should be changed" or "must be announce" rather than "must be announced."

Understanding the Structure:

The structure in question is about the

• modal verb ( should, must, can, could, may, etc.) + be + past participle.

which is known as the passive modal. 

To recall, modals are these verb forms: can, could, may, might, shall, should, will, would, must. Also included are the phrases ought to, used to, need to, had better, and be supposed to. They are all used with other verbs to state possibility, permission, opinion, or intention.

The passive modal is used specifically to make recommendations or instructions,  to state opinions, and sometimes to state rules, such as in the following sentences:

• Recommendation:  The essay's introduction could be revised to include more details about the study's findings. 

• Opinion: I think our company policies should be reviewed to make sure it reflects these new guidelines.
• ​Rule:  All guestrooms must be inspected before the guest can be cleared for checkout. ​

As previously stated, the past participle form of the verb is used with passive modals. The past participle is the form of a verb used with the verb ‘have’ in perfect tenses. For example in the sentence, ‘I have chosen to start over', the word 'chosen' is the verb in past participle form. The past participle is also used with the passive voice. For example in the sentence, ‘It was wrapped in delicate tissue paper’, the past participle verb is 'wrapped'. 

Here are more examples of verbs in their base form and past participle form:

After defining modals and past participles, let's look at examples of mistakes where the writer or speaker forgets to use the past participle when making a passive modal:

1. Should be + past participle
   - Incorrect: "The policy should be change."
   - Correct: "The policy should be changed."

2. Must be + past participle
   - Incorrect: "The decision must be announce to the public immediately."
   - Correct: "The decision must be announced to the public immediately."

3. Can be + past participle
   - Incorrect: "The process can be improve."
   - Correct: "The process can be improved."

4. Will be + past participle​
   - Incorrect: "This issue will be discuss in the next meeting."
   - Correct: "This issue will be discussed in the next meeting."

Recognizing and rectifying errors in the modal + be + past participle structure is fundamental for learners seeking to refine their English language skills, especially since this is a common pattern to use when making recommendations and posting announcements at work.
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Practice this structure by doing the writing activity below:

You're going on a sudden business trip and need to leave instructions to someone about chores that need to be done at your house while you're away.  Use the passive modal structure (modal + be + past participle) to give instructions to this person. 

Examples:

• The houseplants in the balcony must be watered every other day or they will dry out. 
• The dog should be taken out in the morning and again in the evening. 

Enjoy your writing practice and don't hesitate to leave a comment for any questions. ​