The Sentence

Ⅰ. Complete Sentences and Sentence Fragments

A grammatically complete sentence is one that contains at least a subject and a predicate (or finite) verb; if the verb is transitive, there must be an object; if the verb is a link-verb, there must be a predicative or complement:

     He came.
     She wrote a letter.
     Dr. Smith is a professor.

It is important to remember this basic structure of a sentence; otherwise, beginners might make sentences without a subject or a predicate verb or, both, like "Have done it," "Raining," and "How to use it?" instead of "I have done it," "It is raining," and "How do you use it?"
Attributes and adverbials, though they are not essential elements of a sentence, help to make the meaning clear or complete:

     He came to the classroom very early.
     She wrote a long letter to her parents.
     Dr. Smith is a well-known professor of physics.

A complete sentence begins with a capital letter and ends with a period. Again, this simple rule is important for beginners to remember, for in Chinese writing commas may be used to separate complete sentences. The use of a comma in place of a period, a semicolon, a colon, or a dash in English writing is called the comma fault, which Chinese students should be on guard against.

Faulty: It was raining hard, they could not work in the fields.
Improved:
It was raining hard; they could not work in the fields.
It was raining hard. They could not work in the fields.
It was raining so hard that they could not work in the fields.
They could not work in the fields because it was raining hard.
It was raining hard, so they could not work in the fields.
As it was raining hard, they could not work in the fields.

Faulty: I was born in a small town, in the town there was only one school, I studied there for six years.
Improved:
I was born in a small town. In it there was only one school. I studied there for six years.
In the small town where I was born, there was only one school, and I studied there for six years.
I was born in a small town, where there was only one school.
I studied there for six years.
I studied for six years at the only school in the small town where I was born.

The sentences marked "faulty" are not grammatically wrong; they are faulty because of the use of the commas. The two examples contain five short but complete sentences, each of which should have been closed with a period, or a semicolon.
It is easy to see that the improved sentences lay stress on different points. Which one is preferable depends on the context and on the writer's intention.
Here are examples with the semicolon, the colon and the dash:

Faulty: The essay is poorly organized, there is no central idea.
Improved: The essay is poorly organized: there is no central idea.
The essay is poorly organized; there is no central idea.

Faulty: There were people who would be glad to see him leave the place, he knew it.
Improved: There were people who would be glad to see him leave the place, and he knew it.
There were people who would be glad to see him leave the place - and he knew it.

Faulty: The principal of the school may do something to reduce the pupils' homework load, he may, for example, stop assigning homework for Saturday and Sunday.
Improved: The principal of the school may do something to reduce the pupils' homework load - he may, for example, stop assigning homework for Saturday and Sunday.

In fiction, two short sentences closely connected in meaning are occasionally joined by a comma; in expository writing, however, the general rule is to use a period at the end of a complete sentence, whether it is long or short.
It has been said that students should make sentences that are grammatically complete and avoid making sentences without a subject or a predicate verb. But sometimes experienced writers use incomplete sentences for special effect.

It is hard to hear a new voice, as hard as it is to listen to an unknown language....
Why? - Out of fear. The world fears a new experience more than it fears anything. Because a new experience displaces so many old experiences. And it is like trying to use muscles stiff for ages. It hurts horribly.

- D.H. Lawrence

He was, I think, very handsome. I gather this from photographs and from my own memories of him, dressed in his Sunday best and on his way to preach a sermon somewhere, when I was little. Handsome, proud, and ingrown, "like a toe-nail," somebody said.

- James Baldwin

In the first passage three sentences are not complete in structure ("Why?" "Out of fear." and "Because a new experience...") and in the second one sentence ("Handsome, proud..."). We feel that these sentences are forceful: the main idea is made prominent because no other ideas are expressed. But such sentences should be used with care. One could try to use them after one has got some experience in writing.