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Even if a paper has perfect word choice and perfect sentence structure, it can be difficult to understand if the paragraphs are not clearly constructed. Each paragraph must be constructed to tell a story. Readers should be able to recognize the message and follow the story of each paragraph whether or not they understand the science.

For a paragraph to tell a clear story,

  • The ideas in the paragraph must be organized.

  • The continuity, that is, the relationship between ideas, must be clear.

  • Important ideas must be emphasized.


Topic Sentences and Supporting Sentences

General Approach: Overview First, Then Details

A paragraph is a number of sentences on a single topic. The goals of a paragraph are to get a message across and to make the story behind the message clear. These goals can be accomplished in various ways, but the general approach that is clearest for most readers most of the time is to provide an overview first and then to give details. The strategy behind this approach is to create an expectation and then fulfill it.

The reverse strategy is frequently used in scientific papers: here are some details; here is what they mean. In the hands of a master storyteller, this strategy works very well. However, in less expert hands, the details tend to take over. The trees overshadow the forest. The way to avoid this problem is to use a simple, straightforward approach: overview first, then details.

The classic way to give an overview first in a paragraph is to write a topic sentence. A topic sentence is a sentence that states the topic or the message of the paragraph. The topic is what the paragraph is about. The message is the point the paragraph is making. To identify the topic, use a key term. To state a message, use a verb, along with a subject and (usually) a completer.

It is clearest to have only one message per paragraph. Including more than one message in a paragraph makes the paragraph complex and more difficult to understand.

Details that support the topic sentence are written in the remaining sentences of the paragraph—the supporting sentences. The supporting sentences should be organized in a logical way that explains the message of the paragraph.

Examples 3.1, 3.2, 3.3 below all begin with a topic sentence. Each topic sentence names a topic and states a message that makes one (and only one) clear point. In addition, the supporting sentences are organized logically to explain the message stated in the topic sentence, thus fulfilling the expectation that the topic sentence creates.

Example 3.1

AThere are three different theories put forward for the very slow relaxation of catch ...

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