Paragraph unity. Ideally, every sentence in a paragraph should contribute to developing some central idea. The following paragraph would be much better if some portions were removed. Which ones and why?
Probably the greatest advantage of Chicago as the location for our new distribution center is its excellent transportation facilities. The city is served by three major railroads. In fact, Chicago was at one time the hub of cross‑country rail transportation. Chicago is also a major center of the trucking industry, and most of the nation's large freight carriers have terminals there. We are concerned, however, about delivery problems we have had with several truck carriers. We have had far fewer problems with air freight. Both domestic and international cargo services are available at O'Hare International Airport. Finally, except in the winter months, Chicago is a seaport, accessible through the St. Lawrence Seaway.
Paragraph organization. The paragraph above is an example of a classic way of organizing a paragraph: stating a main idea (“excellent transportation facilities”) in the first sentence, and then elaborating that idea throughout the remainder of the paragraph. In this case, the elaborating points are all of equal standing, and could come in any order. In other paragraphs, the points could be ordered chronologically, from greater‑to‑lesser importance (or the reverse), from general to specific, or even spatially (if the paragraph described a physical object). You even can choose an order that places related points closer to the beginning or end of the paragraph to help your transitions from the previous or to the next paragraph. The point is that you should have some reason for the order in which you present things in your paragraph.
Transitions. Transitions are a key to organizing good writing at all levels, from sentences to complete books. They help the reader move smoothly from one sentence (or paragraph, or chapter) to the next and keep track of how the parts relate to each other. In the example paragraph above, several words are italicized. What are each of these words or phrases telling the reader?
Here are some common transition ideas, and a few words that commonly serve each idea.
Result: therefore, thus, hence
Example: for example, specifically, as an illustration
Contrast: but, yet, however, on the other hand
Time: meanwhile, later, after
Sequence: first, then, finally
Pronouns also tie sentences together by referring to a person or thing mentioned previously.
Chaffee & McLeod's study provided a novel way of testing whether watching TV violence causes or is a result of aggression. They...
But you have to be careful—it must be unambiguous who or what the pronoun refers to. In the sentence below, is it the college, the city, or the business district? Letting "college" be the noun of the second sentence would be a better idea.
Midcity College is located in the central business district of the city. It is very large.
Repeating a key phrase or even a word can make the connection. Note the italicized words and phrases in this paragraph, and how re‑using them moves the paragraph along.
Over the past several months, I have heard complaints about the Merit Award Program. Specifically, many employees feel that this program should be linked to annual salary increases. They believe that salary increases would provide a much better incentive than the current $150 to $300 cash awards for exceptional service. In addition, these employees believe that their supervisors consider the cash awards a satisfactory alternative to salary increases. Although I don't think this practice is widespread, the fact that the employees believe that it is justifies a reevaluation of the Merit Award Program.
Paragraph transitions. All the above transition devices can also be used to connect paragraphs with each other. Here's an indirect example relying on the viewer identifying these network names to set up a contrast transition:
. . . five years from now people will get their video content from the Internet and ABC, CBS, NTC, and Fox will be relegated to obscure Web pages. Network officials, for their part, ...
An additional paragraph transition point from the very first example: Notice that the first sentence implicitly contains two related-idea transitions from an earlier paragraphs: “greatest advantage" and "our new distribution center."