This lesson is about sentences and the two most common mistakes students make with constructing sentences. This is not a grammar lesson exactly, but instead a way of thinking about sentences that can help you spot and correct these mistakes. The reason to avoid these mistakes is so that your writing is clearer. This is important not just for the reader, but also for you to use your writing to clarify ideas for yourself.

The first – and the most common – is putting two sentences together as if they are one. These are called “run-on” sentences. The second is making incomplete sentences. The problem is not just in having sentences that are not “grammatically correct”, but in making sentences that a reader would find difficult to follow.

1. Parts of a sentence

Take a simple sentence: “The boy kicks the ball.”

In this sentence you should recognise that we have two nouns (the boy and the ball) and a verb (to kick). The two nouns, however, have a particular relationship to the verb. Here one noun (the boy) does the verb (kicking) to the second noun (the ball).

“The boy” is said to be the “subject” of the sentence. It is the “subject” because it is the active element, the person or thing doing the verb. “The ball” is said to be the object of the sentence. It is the “object” because it is the passive element, the person or thing that is being acted on by the subject doing the verb.

Put simply, in a sentence the subject does the verb to the object. In other words, sentences are about action or activity. In a sentence people or things (subjects) do something (verbs). More often than not they do this to something or someone else (objects). This is true even if sometimes the activity is simply being or existing, for example “He is tall.”

In this example we look at how a thing can be a subject: “The ball falls on his head.”

The subject is “the ball”. The verb is “falls”. The object is “his head”. So the subject doesn’t have to be a person – just the person or thing that is doing the verb.

In this example we look at how a verb can be “passive”: “The ball is kicked by him.”

The subject is “the ball”. The verb is “to be kicked” rather than “kicks”. There is no object. Here the verb has been made passive. The sentence is said to have a “passive construction”. What was described before as the activity (“kicks”) has been replaced instead as a state of being (“is kicked”).  Here the activity (“being kicked”) is being done by the ball.

There is no object here because nothing is being done to him. Instead the “by him” simply counts as a clause or part of the sentence that adds extra information.

It is often clearer to the reader when the verb is used actively. For example journalists would always write “He kicked the ball” rather than “The ball was kicked by him.”

However, where we want to emphasise the effect or the process we will often use the passive construction, for example: “He was stabbed”. In academic writing a passive construction is quite common.

We will look in more detail about how this idea of a sentence helps us in later. But for now there are two rules to bear in mind:

First a complete sentence needs at least a subject and a verb. (There are some exceptions that we will not cover here).

Second two or more of these simple sentences can be combined into one sentence (known as a compound sentence) but this requires connecting words or “conjunctions” such as “and” to clearly separate the subjects and actions described in each simple sentence.

2. Incomplete Sentences

In the previous section we learnt to recognise the parts of a sentence.

To recap, in a sentence we require a subject and a verb. The subject is the person or thing that does the verb. Remember a sentence should convey an action or activity, even if this action is merely existing (the verb “to be”).

Now we can use this information to test whether we have a sentence or just part of a sentence. We will do this by looking at four examples of incomplete sentences.

The first example is:

“Although I got a taste of independent life and what it was like to make my own money.”

This is not a sentence. This is a clause that would modify a sentence. The way that we can recognise this is that nothing is actually being done here.

This becomes slightly clearer if we make it part of a full sentence:

“Although I got a taste of independent life and what it was like to make my own money, I still lacked confidence.”

If we wanted to break this new sentence down we would get:

Although (THIS CONDITION), (SUBJECT) (VERBS) (OBJECT)]

If we remove the word “Although”, it stops being a clause that can be applied to a sentence and starts to be an activity in its own right. So the following IS a sentence: “I got a taste of independent life and what it was like to make my own money.”

The second example is: “Just the simple things like teaching them how to count or read.”

This is not a sentence. Here “simple things like teaching them how to count or read” is a complex noun. There is no verb (i.e. activity or action) being done by a subject in the sentence. You should ask: “Is there an activity of a subject doing a verb being conveyed?”

Our third example is: “Raised in a family oriented culture with two parents and an older sister.”

Here there is no verb again. Here “Raised in a family oriented culture with two parents and an older sister” Is an adverb. Again the test is, “Is there an activity of a subject doing a verb being conveyed?” If we added “He was…” or “I was…” to the start, we would have a sentence.

Our final example is: “Housewife sitting at home raising the children.”

Here we have a compound noun again. Or, our subject is “Housewife sitting at home raising the children”. We have no verb. This is because “sitting” and “raising” are not verbs on their own. They are adverbs – or descriptions – and they need the verb to be or “is” to become part of a verb.

Correct sentences from this might be: The housewife sits at home. / The housewife sitting at home raises the children. / The housewife is sitting at home raising the children. / The housewife sitting at home raising the children longs for action and adventure.

In conclusion, you may not be able to identify all the grammatical terms for the words used. However you should be able to apply a test of whether a sentence is complete by thinking about what the central activity being described is and whether there is the action of a subject on a verb.

Is there an activity here?
Is the sentence describing the action of a subject on a verb?

3. Run on sentences

Run on sentences are one of the most common mistakes found in the construction of sentences. What happens in a run on sentence is that several sentences are run together without a clear separation between the various subjects and verbs. This means that the subject and verb combinations become unclear and the sentence is often difficult for a reader to follow.

The basic rule is that a simple sentence should only have one combination of subject and verb. After that you must start a new sentence. Generally this is done using a full stop and a capital letter. However you can combine two or more sentences using special words called conjunctions.  Examples of conjunctions are:  and / but / or / yet / for / nor / so.  The conjunctions mean that the subject and verb combinations in the different sentences can distinct enough so that meaning is not lost.

Let’s take a simple example: “he throws the ball, she catches the ball.”

This is a run-on sentence. The first subject/verb is “he throws”. The second subject/verb is “she catches”. These do not belong in the same sentence. So we should write: “He throws the ball. She catches the ball.” However, we can combine the two sentences using a conjunction to get: “He throws the ball and she catches the ball.”

We should note that with more than two sentences we can create a list and use a comma and a conjunction. So this is also correct: “He throws the ball, she catches the ball and the game is over.”

We will now look at some more complex examples:

1. a) “I acquired general admin skills as running the office was part of the daily routine, the experience also equipped me to communicate to a team.”

The first subject/verb is “I acquired”. The second subject/verb is “the experience equipped”

A comma is being used where a full stop should be used. It should be: “I acquired general admin skills as running the office was part of the daily routine. The experience also equipped me to communicate to a team.”

1. b) “My biggest achievement to date was buying my flat, at the time I was so green and innocent.”

This is another example of a comma being used where a full stop should be used. It should be:

My biggest achievement to date was buying my flat. At the time I was so green and innocent.

1. c) “As the saying goes, “what doesn’t kill you makes you stronger”, due to the experiences I had I learnt how to deal with small minded people better than others can.”

Here we could join the two with an “and”: “As the saying goes, “what doesn’t kill you makes you stronger” and due to the experiences I had I learnt how to deal with small minded people better than others can.”

Finally we come to a mixed example of run-on and incomplete sentences: “My education consisted of primary and Junior Secondary School at the age of eight to fifteen, and then passed my exams, and had admission to the Senior Secondary School at the age of 16 years.”

The subject of the first part is “My education”, i.e. “My education consisted of ….”. The second part has no subject i.e. the person or thing doing the verb is missing in the last part: “then passed my exams..” The correct sentence should be something like: “My education consisted of primary and Junior Secondary School at the age of eight to fifteen, and I then passed my exams and had admission to the Senior Secondary School at the age of 16 years.”

Or it may be clearer to use a consistent subject: “I went to primary and junior school from age eight to fifteen and then passed my exams to gain admission to the senior secondary school aged 16.”

So, to avoid run-on sentences there are a few things you need to bear in mind:
A simple sentence should only have one combination of subject and verb. After that there must be a new sentence.
To combine two or more sentences you must use a conjunction. Conjunctions include:  and / but / or / yet / for / nor / so.
Try to be exactly clear throughout what subject is doing what verb as you write.