A paragraph is unified when every sentence develops the point made in the topic sentence. It must have a single focus and it must contain no irrelevant facts. Every sentence must contribute to the paragraph by explaining, exemplifying, or expanding the topic sentence. In order to determine whether a paragraph is well developed or not, ask yourself: "What main point am I trying to convey here?" (topic sentence) and then "Does every sentence clearly relate to this idea?"
There are several ways in which you can build good, clear paragraphs. This section will discuss three of the most common types of paragraph structure: development by detail, comparison and contrast, and process. Finally, it will suggest that most paragraphs are built of a combination of development strategies.
Paragraph Development by Detail
This is the most common and easiest form of paragraph development: you simply expand on a general topic sentence using specific examples or illustrations. Look at the following paragraph (you may have encountered it before):
Work tends to be associated with non-work-specific environments, activities, and schedules. If asked what space is reserved for learning, many students would suggest the classroom, the lab or the library. What about the kitchen? The bedroom? In fact, any room in which a student habitually studies becomes a learning space, or a place associated with thinking. Some people need to engage in sports or other physical activity before they can work successfully. Being sedentary seems to inspire others. Although most classes are scheduled between 8:30 and 22:00, some students do their best work before the sun rises, some after it sets. Some need a less flexible schedule than others, while a very few can sit and not rise until their task is completed. Some students work quickly and efficiently, while others cannot produce anything without much dust and heat.
The topic sentence makes a general claim: that school work tends not to be associated only with school. The rest of the sentences provide various illustrations of this argument. They are organised around the three categories, "environment, activities, and schedules," enumerated in the topic sentence. The details provide the concrete examples which your reader will use to evaluate the credibility of your topic sentence.
Paragraph Development by Comparison and Contrast
You should consider developing your paragraph by comparison and contrast when you are describing two or more things which have something, but not everything, in common. You may choose to compare either point by point (X is big, Y is little; X and Y are both purple.) or subject by subject (X is big and purple; Y is small and purple.). Consider, for example, the following paragraph:
Although the interpretation of traffic signals may seem highly standardized, close observation reveals regional variations across this country, distinguishing the East Coast from Central Canada and the West as surely as dominant dialects or political inclinations. In Montreal, a flashing red traffic light instructs drivers to careen even more wildly through intersections heavily populated with pedestrians and oncoming vehicles. In startling contrast, an amber light in Calgary warns drivers to scream to a halt on the off chance that there might be a pedestrian within 500 meters who might consider crossing at some unspecified time within the current day. In my home town in New Brunswick, finally, traffic lights (along with painted lines and posted speed limits) do not apply to tractors, all terrain vehicles, or pickup trucks, which together account for most vehicles on the road. In fact, were any observant Canadian dropped from an alien space vessel at an unspecified intersection anywhere in this vast land, he or she could almost certainly orient him-or-herself according to the surrounding traffic patterns.
This paragraph compares traffic patterns in three areas of Canada. It contrasts the behaviour of drivers in the Maritimes, in Montreal, and in Calgary, in order to make a point about how attitudes in various places inform behaviour. People in these areas have in common the fact that they all drive; in contrast, they drive differently according to the area in which they live.
It is important to note that the paragraph above considers only one aspect of driving (behaviour at traffic lights). If you wanted to consider two or more aspects, you would probably need more than one paragraph.
Paragraph Development by Process
Paragraph development by process involves a straightforward step-by-step description. Those of you in the sciences will recognise it as the formula followed in the "method" section of a lab experiment. Process description often follows a chronological sequence:
The first point to establish is the grip of the hand on the rod. This should be about half-way up the cork handle, absolutely firm and solid, but not tense or rigid. All four fingers are curved around the handle, the little finger, third finger and middle finger contributing most of the firmness by pressing the cork solidly into the fleshy part of the palm, near the heel of the hand. The forefinger supports and steadies the grip but supplies its own firmness against the thumb, which should be along the upper side of the handle and somewhere near the top of the grip. (from Roderick Haig-Brown, "Fly Casting")
The topic sentence establishes that the author will use this paragraph to describe the process of establishing the "grip of the hand on the rod," and this is exactly what he does, point by point, with little abstraction.
Paragraph Development by Combination
Very often, a single paragraph will contain development by a combination of methods. It may begin with a brief comparison, for example, and move on to provide detailed descriptions of the subjects being compared. A process analysis might include a brief history of the process in question. Many paragraphs include lists of examples:
The broad range of positive characteristics used to define males could be used to define females too, but they are not. At its entry for woman Webster's Third provides a list of "qualities considered distinctive of womanhood": "Gentleness, affection, and domesticity or on the other hand fickleness, superficiality, and folly." Among the "qualities considered distinctive of manhood" listed in the entry for man, no negative attributes detract from the "courage, strength, and vigor" the definers associate with males. According to this dictionary, womanish means "unsuitable to a man or to a strong character of either sex."
This paragraph is a good example of one which combines a comparison and contrast of contemporary notions of "manliness" and "womanliness" with an extended list of examples.