A well-written paragraph is said to exhibit cohesion. One sentence has to do with the next, and a collection of such closely related sentences creates a paragraph, one scene or set piece among others which together comprise a document. To cohere means to stick together, and when one sentence adheres to another, our reader sees one idea more richly, more concentratedly, thereby meeting the central requirement of a paragraph: unity.
So how do we write cohesively? That is a technical question and it has a technical, a formal, answer. Let’s begin by looking at a beautifully drawn illustration of cohesion in these two sentences from Carson McCullers’s short story “The Jockey” (quoted here from 50 Great Short Stories, edited by Milton Crane, Bantam, 2005, p.70). These two sentences conclude the first paragraph of the story. A jockey has entered the dining room of a hotel, and is scanning the room “until at last his eyes reached a table in a corner diagonally across from him, at which three men were sitting”:
As he watched, the jockey raised his chin and tilted his head back to one side, his dwarfed body grew rigid, and his hands stiffened so that the fingers curled inward like gray claws. Tense against the wall of the dining room, he watched and waited in this way.
Things are on a slant in this little scene (diagonally and tilted and to one side), and a slant is not normally conducive to the feeling of comfortable order. The first sentence is complicated and involved: grammatically, it is a complex sentence that begins with a subordinate clause, continues with no fewer than four independent clauses, and concludes with another subordinate clause—six clauses in all, designed as what is called a centered sentence, one in which the main elements sit framed by subordinate ones. Such a formidable presentation has the effect of building and piling and mounding a wall of tension that will have to, we suspect, break and give way at some point in the story. It is a grand sentence, and it ends with the foreboding images of curled fingers and curled claws. It ends, that is to say, with threat and tension.
And then how does the immediately next sentence begin? With the very word tense. This adjective begins an introductory phrase that will ultimately modify the subject, he, as we read along, but as we begin the sentence, we really don’t know who or what is tense, and that second of uncertainty only heightens the tension we’ve found ourselves in after reading the first elaborate sentence. Sentences like this second one which begin with a subordinate element in order to delay the main clause and satisfy the thought are called periodic, the word period meaning a circuit or winding path—the long way home to the complete assertion of the main clause. Periodic sentences are also called suspended sentences, because holding back the main thought (he waited and watched) is felt to create suspense.
A periodic sentence stands in contrast to what is called a loose sentence, its inverse. A loose sentence presents the independent clause, the main thought, first, and then lets follow in its train any subordinate elements. Had McCullers composed her second sentence in a loose design (He watched and waited in this way, tense against the wall of the dining room), she would have missed an opportunity to tie so tightly together—to cohere—the idea of tension between the two sentences. Instead, she has left no gap between the images of tension in the first sentence and the continuation of the emotion in the second sentence: she begins the second with a subordinate element in order to name the emotional quality depicted in the first, and that periodic design bridges the two closely and firmly.
Cohesion is an important quality of a paragraph because words and their arrangement carry the risk of deflecting the reader’s attention off onto tangents and angles of only distantly associated ideas. To say the obvious, our mental activity—what the philosophers call mentation—is a powerful force of, it seems, a never-ending energy. The good writer channels that activity with sentences that are connected by their respective design. That creates cohesion, and cohesion unity, and unity vision.