Coherence in a piece of writing refers to the principle that all paragraphs, sentences or ideas in it fit together so well that they form a united whole. Coherent writing has smooth structural, grammatical, and logical movement from one sentence to the next, from one idea to the next, and from one paragraph to the nest. When reading a coherent piece of writing, the reader does not have to pause and guess at the meaning caused by gaps in development between ideas, sentences and paragraphs.
Coherence in English writing exists on two levels -- the overall level and the local level.
Coherence at the overall level means that the information arrangement and structure of a piece of writing should follow the logical thinking and the expectation of the readers, and that the sentences express the meaning that is intended by the context. Although different individuals may have their own opinions about a topic, their expectation and logic of thinking are similar. More specifically, if an author announces that he is writing an essay on sports, which is the context the readers will expect him to discuss athletics, swimming, or ball games, all of which lie within the context of sports. If he unexpectedly goes on with a discussion of economic problems in his home country, the readers will certainly become confused, since the writer is talking out of the context.
Coherence at the local level means that different sentences and paragraphs are logically and smoothly linked to express the intended meaning: the central idea is prominent, the key words are repeated, and the scope of discussion is restricted within the intended range.
The following is an extreme example of an incoherent paragraph:
Yesterday morning, I went to a bookstore. All the foods on the shelf are very fresh and cheap. As my other took some beautiful pieces of furniture home. When I came out of the movie theatre, I found it had snowed in the afternoon.
In the above paragraph, a reader would expect the first sentence to be the context, “I went to a bookstore yesterday”. The reader will then expect an account of what new books he found and bought. However, none of the following sentences refer to the bookstore anymore. Thus, although all the sentences are grammatically correct, they do not form a coherent paragraph and thus fail to convey any coherence meaning.
In Write to Communicate: Practical Writing, it has been mentioned that Chinese is a reader-responsible language while English is a writer-responsible language. The different ways of achieving coherence in Chinese and English again reflect this difference.
Write to Communicate: Practical Writing这本书中提到，中文是“读者负责的”语言，但英文是“作者负责的”语言。这两种语言实现连贯性的不同方式也反应了这种区别。
Chinese relies more on the connection of meaning, including meaning between the lines. Therefore, the Chinese language often leaves the connection of meaning to the readers themselves. When students with a Chinese background write in English, they tend to follow their Chinese way of thinking. On the other hand, English relies more on explicit cohesive devices employed within the flow of the text, in the form of words, phrases, repetition, etc., providing more linguistic and logical information for the reader. If one examines a piece of native English speaker’s writing carefully, one will find that cohesive devices appear almost everywhere in that piece of writing.
Cohesive devices are generally classified into three types.
Refer to the grammatical connections between different sentences. The agreement of tense and number is one of the devices, and parallel structure is another example.
Refer to the connection achieved by the choice of words and phrases, such as the use of pronouns to replace ordinary or proper nouns, the use of synonyms, etc..
Refer to the logical connection among sentences, time relationship, space relationship, cause-effect relationship, etc.. These relationships are usually achieved by adding various adverbs or adverbial phrases in the sentences and paragraphs.
Use pronouns to replace noun or noun phrases.
Napoleon was a great soldier. He was also a great administrator.
He decided to take some heavy shoes with him. He thought that these would be useful in case he went walking.
Use pronominal forms to replace adverbials of time and place.
We called on them soon after breakfast. We should have realised that this was a bad time for a visit.
I decided to take my books back to the library. When I got there, I found it was closed.
Use pronominal forms to replace clauses or sentences.
Some students work all night just before an exam. This is a great mistake.
Repeat the key words.
These train services are not used very much by commuters. As a rule, commuters tend to travel much earlier.
Use synonyms or words of similar meaning to express the same idea.
These cars were first made in 1972. When they were first produced, they were not very popular.
Use constructions implying whole-part or part-whole relationship.
You will need to take some tools with you. You can buy a hammer, a saw, and a screwdriver at any hardware store.
Use related word forms.
Seven people have been arrested so far. The arrests were made late last night.
Use parallel structures.
We hold these truths to be self-evident, that all men are created equal, that they are endowed by their creator with certain unalienable tights, that among these are life, liberty, and the pursuit of happiness.