Supporting sentences further divide the main idea of the paragraph, often into three aspects. The types of supporting sentences appropriate for a paragraph depend on the purpose of the paragraph. Persuasive paragraphs, that is, paragraphs that try to persuade the reader to a certain viewpoint or to make a certain decision, require supporting sentences that back up the validity of the paragraph's argument. Effective informative paragraphs simply break down the main idea of the paragraph. For example, a paragraph arguing that school uniforms suppress individuality would produce three reasons for such a claim, such as the fact that high school is a crucial time when a person explores his own identity. An expository paragraph on the characteristics of an animal could organize information into categories such as habitat, food and behavior.
Often, paragraphs follow a "point-proof-explanation" model. "Point" is another term for supporting sentence. An effective paragraph begins with a clear topic sentence that introduces the main idea, followed by the first point, then a proof and finally an explanation. This point-proof-explanation pattern repeats three times for a total of three points, or supporting sentences.
Merely plunking declarative supporting sentences one after each other creates a choppy, jarring paragraph. Instead, effective paragraphs use transition words to create coherence, or flow, between sentences. Transition words include phrases such as "however," "furthermore" and "additionally." Transition words denote the relationship between different sentences. For example, "however" indicates that a writer is contrasting two ideas, whereas "likewise" signals a comparison.
In addition to coherence, effective supporting sentences aim for unity. Unity means that all the sentences in a paragraph stick to the same topic. Digressions, when a writer introduces an idea only tangentially related to the driving idea of the paragraph, confuse and disorient a reader. They also weaken a paper's authority.