Common Errors in Grammar

For a sentence to be complete, you need to have a subject and a predicate. The subject is a thing, animal or person. The predicate tells us what the subject is doing, or what state it is in. The predicate must contain a verb that is in the finite form (a form that indicates time and does not just have ‘to’ in front of it). The parts of a sentence should work together so they form a complete idea or thought that can stand alone.

In a sentence fragment, one of the key components is missing: it does not have a subject, it does not have a verb or verb phrase, or there is not a complete idea.

Below are some examples:

‘While the second result was positive.’ – This is what is known as a ‘dependent clause’ and more information is needed to form a complete idea. Here is a possible solution:

‘While the second result was positive, the rest of the results were inconclusive.’

‘The journalist in the first office.’ – This is a sentence fragment as it does not have a verb and is not a complete idea. Here is a possible solution:

‘The journalist in the first office was called Jane.’

‘Running in the park.’ – This is could be a sentence fragment either because the verb or verb phrase is missing or because the verb phrase is incomplete. This means there is more than one solution:

‘Running in the park is good for you.’ (Here the subject is ‘running’ and the verb is ‘is’.)

‘She was running in the park.’ (Here the subject is ‘she’ and there is a verb with two words: ‘was running’).

For more information, check out our guide Top Tips for Sentence Writing.

Both the comma splice and run-on sentence are common errors in writing. They are to do with inappropriate punctuation, or a lack of punctuation, between two or more independent clauses. Independent clauses are pieces of text that could be sentences on their own. You can think of them as complete ideas. They will have a subject (a person or thing) and piece of text that says something about that subject (known as the predicate).

Comma Splice

A comma splice is where a comma is used to separate two independent clauses. In order to separate two independent clauses, you will need to use a full stop, coordinating conjunction, such as ‘and’, or a semicolon. The following is an example with a comma splice:

"The death rate decreased between 1977 and 1999, the health care system improved dramatically over this time period." – Incorrect

Here are the options to correct the sentence:

"The death rate decreased between 1977 and 1999 as the health care system improved dramatically over this time period." – Correct

"The death rate decreased between 1977 and 1999. This was a result of the health care system improving dramatically over this time period." – Correct

"The death rate decreased between 1977 and 1999; the health care system improved dramatically over this time period." – Correct

Tip: If you can use a full stop, it is the wrong place for a comma.

Run-On Sentence

A run-on sentence is where two independent clauses have been joined without any punctuation or linking words between them. As noted above, independent clauses are pieces of text that could be sentences on their own. As with a comma splice, you need to add in a full stop, coordinating conjunction or semicolon to fix this problem. Here is an example of a run-on sentence:

"Smoking near other people is now often judged as inappropriate behaviour this was not the case around 20 years ago before the smoking ban."

Hopefully you can see that there are two independent clauses (or complete ideas here). You can see these marked with the numbers below:

"(1) Smoking near other people is now often judged as inappropriate behaviour (2) this was not the case around 20 years ago before the smoking ban."

Here is a possible correction using the coordinating conjunction ‘but’:

"Smoking near other people is now often judged as inappropriate behaviour, but this was not the case around 20 years ago before the smoking ban."

For more information, check out our guide Tips and Tricks for Using Punctuation.

Sentences can be broken into two main parts: a subject and a predicate. The subject is a thing, animal or a person. The predicate tells us what the subject is doing, or what state it is in. The predicate must contain a verb that is in the finite form (a form that indicates time and does not just have ‘to’ in front of it). The subject and predicate together will form a complete idea to make a sentence.

Here are some examples to illustrate this:

In the sentence ‘I went to work.’ ‘I’ is the subject and ‘went to work’ is the predicate. The verb in this sentence is ‘went’, which is the past tense of ‘to go’. One common error that people make in writing is to put a comma between the subject of the sentence and the main verb. The following is an example of this:

"The very large population of the country, resulted in a strain on the water resources."

In the example above, the subject is ‘the very large population of the country’ and the predicate is ‘resulted in a strain on the water resources’. The verb is ‘resulted in’ (the past tense of ‘result in’) There is no need for a comma in this sentence and it should be removed. To avoid this error, check your use of commas carefully when you proofread your documents. Make sure you do not have commas between the subject and the verb associated with that subject in any sentences.

For more information on the use of commas, check out our guide Top Tips for Using Punctuation.

Semicolons and colons have different jobs. A semicolon is used to separate two independent clauses (two complete ideas that could be sentences) that are closely related or it is used to separate items in a list. A colon is used when further explanation or information is needed after a complete statement. A colon is often used to introduce lists. You do not always need to have an independent clause (complete idea) before a colon.

Frequently, people use a semicolon to introduce a list where they should use a colon. The following is an example of this:

"There are several reasons why spending time on writing an introduction is a good idea; it is the first part of your work people read, it gives background information and it sets the direction of your work."

The correct version needs to have a colon instead:

"There are several reasons why spending time on writing an introduction is a good idea: it is the first part of your work people read, it gives background information and it sets the direction of your work."

In some cases, you might want to combine the use of colons and semicolons. This is particularly useful when you have lists within lists where the use of more commas between the items could confuse the reader. The following is an example of this:

"There are three major government departments in one area of the city: the department for trade, business and enterprise; the department for the environment, food and farming; and the department for energy and climate change."

For more information on the use of colons and semi-colons, check out our guide Tips and Tricks for Using Punctuation.

Sentences can be broken into two main parts: a subject and a predicate. The subject is a thing, animal or a person. The predicate tells us what the subject is doing, or what state it is in. The predicate must contain a verb that is in the finite form (a form that indicates time and does not just have ‘to’ in front of it). The subject and predicate together will form a complete idea to make a sentence.

The subject of the sentence and the verb of the sentence must agree in number. This means that if you have a singular subject, the verb must also be in a singular form. If you have a plural subject, the verb must also be in a plural form. This occurs in tenses that use present tense verbs.

In order to understand this, we also need to know about the different subjects that can appear in the sentence. The table below explains this:

For sentences that use the third person singular as a subject, the singular form of the verb is needed. In this case an ‘s’ is added to the verb (in the case of regular verbs). The following is an example of this using the subject ‘John’ and the verb ‘run’:

"John runs every day."

With plural subjects and the first and second person singular we do not add ‘s’ to the verb. The following is an example using the plural subject ‘students’:

"The students run every day."

Not all verbs conform to the rule of adding an ‘s’ for plural. These verbs are known as irregular verbs and they will change more dramatically depending on what subject is being used. You have to know which verbs are irregular to choose the correct form based on the subject. This is illustrated with the verb ‘to be’ in the following table:

Although subject-verb agreement might seem like quite a basic grammar point, it can be hard to know whether or not to use a singular or plural verb for the subject in some cases. For example, although the word ‘everyone’ represents more than one person, you use a singular verb with an ‘s’ added. Another more tricky case is when the subject has two or more items joined with ‘and’; in this case you use the plural form of the verb.

There is a good explanation of the rules for subject verb agreement on the following website: Subject-Verb Agreement - Grammar - Academic Guides at Walden University

The articles in English are ‘a’, ‘an’ and ‘the’. Articles help us determine what it is we are talking about. People often select the wrong article when writing, or do not use one when they should. We can classify the articles in English as definite or indefinite. The definite article is ‘the’. The indefinite articles are ‘a’ or ‘an’. We use ‘an’ when the noun following the article begins with a vowel sound and ‘a’ when it begins with a consonant sound. In some cases, you do not need an article before a noun. Sometimes this is referred to as the ‘zero article’.

The definite article ‘the’ is used when we want to talk about a definite/specific thing. In this case, there will only be one in existence, or you, or the person you are talking to, know which specific thing you are making reference to.

The indefinite articles ‘a’ and ‘an’ are used to introduce or refer to something in general.

No article/the zero article is used when we are referring to a countable plural noun or an uncountable noun in a general sense (see the explanation below the table if you do not know what countable and uncountable nouns are). The table below summarises these rules:

A countable noun is a noun that can be counted. For example, the noun ‘tree’ is countable as we can put a number in front of it, such as three trees. We turn the noun into a plural, which in this case is done by adding an ‘s’.

Uncountable nouns are nouns that cannot have a number in front of them and cannot be plural. An example would be with the word ‘information’. We cannot say ‘two informations’. Instead we would say something like ‘two pieces of information’.

If you would like more practice of using articles, then please consider signing up to the CAS Grammar Basics E-Learning course, which has a lesson on articles.

Some prepositions always go with certain words to create a phrase. For example, the adjective ‘associated’ is normally used with the preposition ‘with’ followed by a noun. Here is an example of this use:

"Smoking is associated with poor health."

There are many other phrases that are made with a preposition. The phrases could also take the pattern of noun + preposition or verb + preposition. In order to use prepositions correctly, it can be useful to learn the patterns as there are no particular rules. You can note phrases down when you see them in texts and then come back to test yourself. Also, the more you read, the more comfortable you will feel with choosing the correct preposition.

The .pdf document from the University of Canterbury in New Zealand, available from the link that follows, has a list of different dependent preposition patterns with examples that would be useful to learn to help with writing: DPP (canterbury.ac.nz)

There are also many places online where you can get extra practice; you just need to search ‘dependent prepositions practice’.

When writing, we often use two or more phrases or clauses together that have a similar length or are the same grammatical form (for example, all nouns). This is also known as parallelism or using parallel structures. Faulty parallelism occurs when one phrase or clause differs in form from the others it is being used with. People often make this mistake with items in a list. Here is an example:

‘The house needs further design work, planning work and to order the materials.’  

The first two items in the list are nouns, while the last item is a phrase that starts with a verb (to order). Here is how this mistake could be corrected:

‘The house needs further design work, planning work, and work to order the materials.’

In the corrected sentence the third item in the list has been changed to make it a noun phrase (the phrase is based on a noun). To avoid this error, always carefully check any lists that you include in your writing when you proofread to make sure the items in the list are the same grammatical form.

Sentences help to break writing into chunks of text that a reader can understand. They represent a complete idea, and are made of sections known as ‘clauses’. There are no definite rules for the length of a sentence, and you should aim to have both long and short sentences in your writing. However, sometimes writers will produce very long sentences with lots of clauses where the reader may get lost. This normally occurs when a writer joins too many clauses using coordinating conjunctions (such as ‘and’), or relative pronouns (such as ‘which’), or ‘ing’ words.

Here are some examples of this:

Example 1

"A good level of education is seen as vital across the globe, meaning that governments invest in it heavily, resulting in it competing for budget with other essential services."

Example 2

"When new developments are built, local infrastructure that has become outdated may require improvements, which may include changes to roads, schools and parks, and these changes can be very costly."

To solve this you can break up the sentences to form new sentences. You can also use words that recap or repeat the idea mentioned in the previous clause. Here are some examples of how these solutions could be used in the sentences above:

Example 1

"A good level of education is seen as vital across the globe. (new sentence) This means that governments invest in it heavily, a policy (recap word that summarises the idea in the previous clause) which results in education competing for budget with other essential services."

Example 2

"When new developments are built, local infrastructure that has become outdated may require improvements, improvements (repeat word) that may include changes to roads, schools and parks, which can be very costly." 

We often use pronouns (such as ‘it’ ‘this’ ‘he’ or she’) to refer to something or someone when we do not want to repeat the name of the thing or person in the next sentence. This is a good thing as it means we do not have to repeat the same word many times in a piece of writing. However, when a sentence is talking about two or more different things or people, the use of pronouns in the following sentence or sentences can cause confusion if it is not clear who or what the pronoun is referring to.

Here is an example of this:

‘The experiment found that the change in the colour of the plants could be due to nutrients in the soil. It is best illustrated through the use of a diagram.’

In the sentence above we do not know if the ‘it’ in the second sentence is referring to ‘the experiment’ or ‘the change in the colour of the plants’. To make sure the reader does not get confused, it may be best in this case to repeat a word or use a ‘recap’ word that clarifies what we are talking about. Here is an example of one possible solution:

‘The experiment found that the change in the colour of the plants could be due to nutrients in the soil. This result is best illustrated through the use of a diagram.’

To avoid the problem of using unclear pronouns, look out for where you have used pronouns in the text when you proofread. Where you have used them, check that the reader will be able to tell who or what you are referring to. This problem is particularly common with the words ‘it’ and ‘this’, so you could search your document for these pronouns using the Ctrl+f function on your computer and check that your sentences are totally clear.

A modifier is a piece of text that adds extra information about something or someone in a sentence. For example, it might be information about where, when or how something was done or how someone behaved or felt.

Misplaced Modifiers

If a modifier is used in the wrong place, or is too far from the thing it is describing, it can be hard to tell what the modifier is referring to. Here is an example, taken from a student text, of where a misplaced modifier has been used: 

‘The reason for choosing this topic is that smoking cigarettes is one of the leading causes of multiple organ dysfunction diseases and cancer, which is a habit that is common around the world.’

In this example the modifier is ‘which is a habit that is common around the world’. The problem is that where the modifier is located, at the end of the sentence, means that it seems like it is referring to ‘multiple organ dysfunction diseases and cancer,’ when actually it is referring to smoking. To correct this error, the modifier needs to be moved so it is clearly associated with smoking. Here is a possible correction:

‘The reason for choosing this topic is that smoking cigarettes, which is a habit that is common around the world, is one of the leading causes of multiple organ dysfunction diseases and cancer.’

Here is another example:

‘The patient sat down on the chair seeming distressed.’

This example is perhaps less obvious, but in this case it is not clear if it is the chair or the patient who is distressed. A possible correction for this would be the following:

‘The patient, seeming distressed, sat down on the chair.’ 

Dangling Modifiers

A dangling modifier is slightly different from a misplaced modifier. In this case, the thing that the modifier is referring to is missing from the sentence. Here is an example of this:

‘After being repaired, Pippa drove home.’

In the sentence above, it is not clear what the first clause is referring to. To fix this, you could mention ‘the car’ in the first clause and change the tense slightly. Here is a possible solution:

‘After the car had been repaired, Pippa drove home.’

Misplaced and dangling modifiers can be identified through careful proofreading. Look for pieces of text where you have added extra information to explain or describe something further. If you do find any modifiers, make sure it is clear what those modifiers are referring to. Dangling modifiers occur frequently when people use participles to try to describe something. These are words that will have ‘ing’ or ‘ed’ on the end. You should double check that you have used these words appropriately if you find them in any modifiers that you have written.

It can be hard when to know to include commas in a text. Often people use too many commas in a sentence; however, in some cases, people leave commas out of a sentence when they are needed. This often occurs when people want to add a parenthesis. A parenthesis is a piece of text that adds additional information to a sentence that is useful but not needed for the sentence to make sense. This information needs to be separated off by commas from the rest of the text. Here is an example of commas being used correctly for this purpose:

"The new building, being very well designed, is a popular place for students to go."

The sentence is referring to a building that has been newly completed and is well designed. If we removed the information in between the pair of commas, the sentence would still make sense. If we remove the commas entirely from this sentence, the meaning of the sentence would be different. It would suggest that the building is in the process of being designed. In this case, the sentence would not really make sense.

Here is an example where the parenthesis is at the end of the sentence:

"The ship came ashore at the base of the cliffs, making it a total wreck."

Again, in this example, the information at the end is not needed for the sentence to make sense, but it does add useful information and the sentence may be slightly confusing if the comma were to be removed. When you add additional information like this to a sentence, which is not required for the sentence to make sense, make sure you separate it off from the rest of the text using commas. You can check for this when proofreading by scanning for where you have used commas and checking to see if you have used them correctly.

For more information on the use of commas, check out our guide Tips and Tricks for Using Punctuation.

Apostrophes are needed to indicate ownership of something. Here is an example:

"The girl’s bag was on the floor."

The ‘apostrophe + s’ indicates the bag is owned by the girl. There are a few things you need to pay attention to when using apostrophes to indicate ownership of things:

Rules for Using Apostrophes

If you have a plural, then you can put the apostrophe behind the s:

"The girls’ bags were on the floor" (there is more than one girl and more than one bag in this case)

If the noun you are using ends in an ‘s’, then normally you will add ‘s:

"Chris’s bag was on the floor."

However, there is some debate over whether this is needed, and in some cases writers and editors will not add an additional ‘s’ if the noun is a proper noun (such as the name of a person). It is probably best to choose one option and be consistent. More information on this is available here: Apostrophes with Words Ending in s - The Blue Book of Grammar and Punctuation (grammarbook.com)

You do not need an apostrophe with a possessive determiner and pronoun:

Words like "your", "its" and "whose" already indicate ownership. In some cases it may confuse the reader when an apostrophe is used with these words. For example, the structure “it’s” is a contraction and means ‘it is’. Here is an example:

"Its straps were broken." – Correct

"It’s straps were broken." – Incorrect

An apostrophe + s can be added to a whole phrase:

"Hannah and Dave’s house is red." – In this sentence, both Hannah and Dave own the house.

You may need two or more apostrophes when using a string of nouns together:

"Mary’s husband’s hair is blonde."

In this case we need to indicate ownership between Mary and her husband and Mary’s husband and his hair. Once you become familiar with the rules for apostrophes, they become easier to use. However, these are also things you can scan for and check when proofreading.