Fragments are a common mistake. A sentence must have a subject and a verb.
- The students worked hard. (Subject – the students; verb – worked)
- She wrote a story. (Subject –she; verb – wrote)
- They discussed the problem. (Subject – they; verb – discussed)
A group of words that does not have a subject and a verb of its own cannot be a sentence. It is merely a sentence fragment or a phrase. Note that a sentence fragment cannot stand on its own. It must be attached to a sentence.
The subject of a sentence is usually a noun or a pronoun. Infinitives and gerunds can also act as subjects.
Verbs can be confusing. There are mainly two types of verbs: finite verbs and non-finite verbs. A non-finite verb is an incomplete verb. It cannot make a sentence. Examples of non-finite verbs are: infinitives (to work, to sing, to break, to walk), participles (working, singing, breaking, walking) and gerunds (dancing, waiting, reading etc.)
As you can see, participles and gerunds look alike, but they have different grammatical properties. Participles act like adjectives. Gerunds, on the other hand, act like nouns.
Study the group of words given below. It does not make a sentence because the verb (playing) is incomplete.
- The children playing in the park.
To make the verb playing complete, we have to add a suitable auxiliary verb.
- The children were playing in the park.
An English verb has four forms: the infinitive, the past simple, the present participle and the past participle.
Infinitives are forms like sing, dance, read and write. They are used to make the simple present tense. The infinitive is sometimes preceded by the marker to. In this case, they are called to-infinitives. Note that a to-infinitive is a non-finite verb. It is an incomplete verb. Without the marker to, the infinitive can function as a complete verb.
The past simple
This is the form of the verb used to make the simple past tense. Examples are: sang, danced, read and wrote. The past simple is a complete verb.
The present participle
The present participle ends in –ing. Examples are: singing, dancing, playing, working etc. The present participle is an incomplete verb. To make it complete, you have to add a form of be (is, am, are, was, were).
Examples are: was writing, were playing, am working, is singing etc.
The past participle
The past participle is an incomplete verb. It usually ends in –ed or –en. Examples are: worked, written, broken etc. To make it complete, you have to add a form of have. Note that in the case of most verbs, the past simple and past participle forms look alike.
The verb forms given below are complete.
- Have worked
- Has waited
- Had written