If the subject on which you are writing is of slight extent, or if you intend to treat it very briefly, there may be no need of subdividing it into topics. Thus a brief description, a brief summary of a literary work, a brief account of a single incident, a narrative merely outlining an action, the setting forth of a single idea, any one of these is best written in a single paragraph. After the paragraph has been written, examine it to see whether subdivision will not improve it.
Ordinarily, however, a subject requires subdivision into topics, each of which should be made the subject of a paragraph. The object of treating each topic in a paragraph by itself is, of course, to aid the reader. The beginning of each paragraph is a signal to him that a new step in the development of the subject has been reached.
The extent of subdivision will vary with the length of the composition. For example, a short notice of a book or poem might consist of a single paragraph. One slightly longer might consist of two paragraphs:
A report on a poem, written for a class in literature, might consist of seven paragraphs:
The contents of paragraphs C and D would vary with the poem. Usually, paragraph C would indicate the actual or imagined circumstances of the poem (the situation), if these call for explanation, and would then state the subject and outline its development. If the poem is a narrative in the third person throughout, paragraph C need contain no more than a concise summary of the action. Paragraph D would indicate the leading ideas and show how they are made prominent, or would indicate what points in the narrative are chiefly emphasized.
A novel might be discussed under the heads:
An historical event might be discussed under the heads:
In treating either of these last two subjects, the writer would probably find it necessary to subdivide one or more of the topics here given.
As a rule, single sentences should not be written or printed as paragraphs. An exception may be made of sentences of transition, indicating the relation between the parts of an exposition or argument. Frequent exceptions are also necessary in textbooks, guidebooks, and other works in which many topics are treated briefly.
In dialogue, each speech, even if only a single word, is a paragraph by itself; that is, a new paragraph begins with each change of speaker. The application of this rule, when dialogue and narrative are combined, is best learned from examples in well-printed works of fiction.
Again, the object is to aid the reader. The practice here recommended enables him to discover the purpose of each paragraph as he begins to read it, and to retain this purpose in mind as he ends it. For this reason, the most generally useful kind of paragraph, particularly in exposition and argument, is that in which
(a) the topic sentence comes at or near the beginning;
(b) the succeeding sentences explain or establish or develop the statement made in the topic sentence; and