The act of providing convincing data or groundwork leads the reader to the topic sentence, which then also serves as the conclusion. The following sample paragraph is an example of one in which the topic sentence and controlling idea appear in the final position: People do it everyday. Matt Ellis Updated on June 2, 2022 Students A topic sentence, usually the first sentence in a paragraph, introduces the main idea of that paragraph and sets its tone. A topic sentence is especially important in essays, where topics change from paragraph to paragraph. I. What is a Topic Sentence? A topic sentence in a paragraph is like the GPS in a car. It shows you (and others) where you are going and explains the point of the paragraph. Everything else is used as supporting details. The topic sentence contains two parts: the topic and a controlling idea. 0hkm5J.