An important factor in determining paragraph coherence is the number of links among sentences created by pronouns, synonyms, and by the repetition of key words and phrases. A sentence will have links leading to it from preceding sentences and links leading from it to succeeding sentences. The total number of links leading to and from a sentence is a measure of how firmly it is embedded in the network of concepts that make up the message of the paragraph. This idea is illustrated in the paragraph below. The sentences are numbered and listed to facilitate discussion. The initial use of a key word is highlighted in orange and its subsequent appearances are indicated in blue.

The key word "ear" appears in different contexts in different sentences: "middle ear" in one, "ear canal" and "middle-ear bones" in two, and "inner ear" in six. However, these differences are not significant since in each case the general context is the same: ear architecture. The differences in the specific contexts therefore yield to the semantic identity of the more general concept and justify the use of "ear" alone as a key word that links the sentences.

A flow chart is one possible way to represent the network of relations among the sentences in a paragraph. However, the number of links among the sentences for even this short paragraph is quite large (30), making a clear chart difficult to create. But, the links among the sentences can be tabulated in two ways: First, starting with the topic sentence and counting the number of times each key word appears in subsequent sentences shows the links out of each node of the network. Alternately, beginning with the last sentence and counting the number of times each key word appears in preceding sentences shows the links into each node of the network. The following tables illustrate these options.

In each, the sentences are numbered in the first column. The columns to the right list the key words that appear in each sentence. The numbers in parenthesis in Table One identify the preceding sentences in which the key words appear or are represented by a pronoun, and in Table Two the subsequent sentences in which the key words are repeated. Each repetition of a key word or the substitution of for a key word creates a link.

These tables indicate that the links among the sentences in a paragraph are not just connected in a sequence but form a network. For example, looking at Table One, consider the word "stapes." It appears in sentences two and three and in sentences five and six, making direct connections between these pairs. However, the repetition of the word also connects sentences two and five, three and five, two and six, three and six , and five and six. The multiple relations tighten the cohesion of the text by reminding the reader of the previous contexts of the word and bringing these to bear on his understanding of the word at each new appearance.

Each sentence in the paragraph might be compared to an airline hub which serves as a transit point for travelers on route from one destination to another. Travelers may arrive from a single point of origin or from a number of different points, and from the hub depart to a variety of destinations. The following table lists the number of links to and from the sentences in the sample paragraph.

The table shows that sentence two is an important hub sentence. Although it has only one link in from the topic sentence, it makes first mention of four of the key terms that are repeated in subsequent sentences and provides eight links out.

The most certain way for a writer to maintain coherence is to make sure that every sentence has at least one link with the sentence that immediately precedes it. However, as the paragraph illustrates, this kind of sequential linking does not always occur. Sentence four above is not directly connected to sentence three.

Although the word "bone" does in fact appear in both sentence three and sentence four and would appear to provide such a link, the referrent in each case is different. In sentence three, "bone" is used in reference to the growth which encapsulates the stapes and keeps it from functioning, while in sentence four, the referrent is to the hammer, one of the articulated bones of the middle-ear. It is reasonable to assume that the distinction is recognized by the sematic component of the grammar's deep structure. If not confusion would result, and this is not the case for even a moderately attentive reader.

In addition, coherence is not disrupted because two factors compensate for the lack of an explicit link between sentences three and four. First, sentence four is connected to the network by multiple links; it has two links in and two links out, being connected to sentence two by the key words "ear" and "bones," to sentence five by "hammer," and to sentence six by "ear."

Furthermore, the relationship of sentence four to the rest of the paragraph is sustained by a redundancy of implicit relations among all the sentences. In sentence four, "sound waves," "travel," and "strike" make implicit references to the subjects of hearing and ear architecture and thus provide invisible threads to bind the sentence to the key words and their related terms in the other sentences.

This example illustrates how relations among sentences in a paragraph constitute a network. The network incorporates linear sequences, but these are incomplete parts of the multiple and complex relations that characterize any coherent discourse. A message is not understood by adding up the meanings of a chain of words, or a chain of sentences, but is derived from the comprehension of redundant and mutually supportative concepts carried by grammatical structures that determine their relations.

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