The main idea is the writer or speaker’s most important idea or point. A supporting detail is a piece of information that gives more information about the main idea. It is very useful to understand main ideas and supporting details. In reading and listening, thinking about them can help you to understand more easily. You can make your writing clear by following conventions1 about main ideas and details, which you will learn in this unit. In writing, main ideas and supporting details usually go together in the same paragraph. A paragraph expresses or develops one main idea with supporting details. There is usually a blank line separating each paragraph, but sometimes the first word of a paragraph is indented instead—that is, the first line of the paragraph starts with some space before it.