In paragraphs, your main point is expressed in a topic sentence. In both paragraphs and essays, it is important to add enough details (secondary support) about the primary support to make the main point clear to readers.

In the following paragraph, the topic sentence is underlined twice, the primary support is underlined once, and the details for each primary support point are in italics.

When I first enrolled in college, I thought that studying history was a waste of time. But after taking two world history classes, I have come to the conclusion that these courses count for far more than some credit hours in my college record. First, learning about historical events has helped me put important current events in perspective. For instance, by studying the history of migration around the world, I have learned that immigration has been going on for hundreds of years. In addition, it is common in many countries, not just the United States. I have also learned about ways in which various societies have debated immigration, just as Americans are doing today. Second, history courses have taught me about the power that individual people can have, even under very challenging circumstances. I was especially inspired by the story of Toussaint L’Ouverture, a former slave who, in the 1790s, led uprisings in the French colony of Saint-Domingue, transforming it into the independent nation of Haiti. Although L’Ouverture faced difficult odds, he persisted and achieved great things. The biggest benefit of taking history courses is that they have encouraged me to dig more deeply into subjects than I ever have before. For a paper about the lasting influence of Anne Frank,¹ I drew on quotations from her famous diary, on biographies about her, and on essays written by noted historians. The research was fascinating, and I loved piecing together the various facts and insights to come to my own conclusions. To sum up, I have become hooked on history, and I have a feeling that the lessons it teaches me will be relevant far beyond college.

In an essay, each primary support point, along with its supporting details, is developed into a separate paragraph. (See the diagram in “The Writing Process” in Chapter 2.) Specifically, each underlined point in the previous paragraph could be turned into a topic sentence that would be supported by the italicized details. However, in preparing an essay on the preceding topic, the writer would want to add more details and examples for each primary support point.