Paragraphs will nearly always contain a sentence that indicates the idea around which the paragraph is built. This sentence is called a topic sentence. Note that the word “topic” can be misleading here. These sentences indicate the idea of the paragraph, not simply the topic. In other words, they indicate the point of the paragraph or what the paragraph is trying to say, not just what the paragraph is about. If you don’t have a strong topic sentence, it may be that the paragraph isn’t focused on a single idea.
Topic sentences are usually at the beginning of a paragraph, but they don’t have to be. You may choose to hold off indicating the point of a paragraph until the middle or even the end of that paragraph. For example, there may be a reason that you would prefer to build up to a point rather than state it at the outset. This is a viable strategy, but it’s important to consider why you’re choosing it. Note that the reader will not be able to tell what your point is until you get to it, so you should be sure that using this alternative is preferable to a more straightforward structure, where the topic sentence is placed at the beginning.
The job of the rest of the paragraph then is to support that topic sentence. This can mean various things, depending on the nature of the topic sentence. The rest of the paragraph might provide reasons to believe whatever the topic sentence claims.
Or perhaps it will explain a concept introduced in the topic sentence. It may instead offer examples of the idea that the topic sentence presents. Generally speaking, the rest of the paragraph exists to address whatever was set up by the topic sentence.
In most cases, the relationship between the topic sentence and the rest of a paragraph will be very similar to the relationship between your thesis statement and the rest of the paper. A strong thesis statement will make the reader interested in what you have to say. This is primarily a matter of creating questions in the mind of the reader. Is that true? Why is that the case? How does that work? Then, the rest of the paper provides answers to those questions. Strong topic sentences will set up similar, but more focused and narrow questions in the reader’s mind. The job of the rest of the paragraph, then, is to satisfy the reader’s questions.
Occasionally, it may be necessary to have a topic sentence that establishes multiple points that you will address in the next few paragraphs. For example, you may have a list of supporting details that you want to explore, and it’s preferable to introduce them all at once. This is perfectly acceptable. However, you should separate the ideas into their own paragraphs and address them one by one.
In revision, look for topic sentences that are too broad or that set up multiple ideas. Could they be broken into multiple paragraphs or focused in order to provide a deeper exploration of your ideas? Doing this can increase the depth and impact of your writing and provide a more thorough and satisfying reader experience.
For more clarity on this subject and to see an example of a successful topic sentence, check out the Paragraph Structure handout by visiting the Writing Center’s Resource Library at: https://www.rockvalleycollege.edu/StudentServices/Tutoring/WritingCenter.cfm