In writing, most paragraphs are composed by three main sections the first one is the topic sentence that is usually the first sentence in a paragraph and states in general terms the content and purpose of the paragraph; the second section is the supporting details that can include statements, reasons, evidence, examples, etc. and develop the topic sentence and the third section is the conclusion, which summarizes and closes the paragraph. Therefore, the purpose of a paragraph is most clearly expressed in the topic sentence.
