How to write good topic sentences
If argumentative essays were newspaper articles, thesis statements would be the headlines—and as a thesis statement is like the headline of an essay, a topic sentence is like the headline of a paragraph. This is because, like the thesis, they let the reader know what to expect.
Topic sentences have three basic functions:
- Describe all and only the topic matter of the paragraph.
- Clearly situate the paragraph’s content in relation to the thesis.
- Provide a transition from the preceding paragraph.
1. How much topic matter to cover with a topic sentence
All and only
Though small, the words “all” and “only” are both very important here. The first requires your topic sentence to cover enough information, while the second limits the amount of information the topic sentence should cover.
All of the information in the paragraph should relate clearly to the topic sentence. This means, reciprocally, that the topic sentence should be just broad enough to account for, with some detail, all the points you make in the paragraph. Make sure the topic sentence is sufficiently expansive and precise. To help with this, use key words from the most important point(s) you make in the body of the paragraph.
However, only the information in the paragraph should be covered by the topic sentence (except in the case of compound topic sentences). This means that the topic sentence should not be any broader than the topic matter in the paragraph requires.
Thinking of these all and only requirements, consider your topic sentence to present a miniature mirror-image of the paragraph’s content. Everything you see in the paragraph you should also see in the topic sentence; on the other hand, usually, information that you don’t see in the paragraph you should not see in the topic sentence.
When revising your paragraphs, if you notice a difference between what the topic sentence covers and what the paragraph covers, you always have two options: change the topic sentence or change the paragraph. Perhaps you will need to carefully add a few words to the topic sentence; or perhaps something important is missing from the paragraph, and you will need to add that. On the other hand, perhaps your topic sentence is too broad, and you need to cut something from it; or perhaps your paragraph covers information irrelevant to the topic sentence, and you need to delete that information or find it a new home.
Compound topic sentences
Sometimes a topic sentence works more like a section introduction, outlining information that will come over the next two or three paragraphs. In this case, you should use two topic sentences in the same paragraph, what we might call a compound topic sentence. The first of the two is the section-heading-like topic sentence—the same “all and only” rules apply to this topic sentence, but it covers a few paragraphs’ worth of information. The second topic sentence picks up one part of the first and covers all and only the information in the present paragraph.
Example Compound Topic Sentence
[First T.S.] The government has three main obstacles to developing tidal hydro power on the coast: funding, location, and technological innovation. [Second T.S.] The problem of funding results from prior financial commitments and the relatively low budget of the province.
The present paragraph would continue to discuss funding, while the next paragraph would take up location, starting with another topic sentence.
2. Connection to the thesis or overall argument
Covering only the first basic function, the topic sentence is incomplete. We might know what the paragraph is about, but we need to know why this information is important to the main point of the essay. The second function of the topic sentence clarifies this matter—connect the topic sentence to the thesis.
To ensure that your topic sentences fulfill this second function, ask yourself, “How does this paragraph help the reader understand why my thesis is right? How can the reader identify the connection between the point I make here and the overall point that I earlier set out to make?” Answers to these questions should be obvious from the topic sentence.
To help ensure these connections are clear, re-use key words that you’ve used in your thesis, and make sure that you are explicit about how the paragraph explores the larger point. To illustrate, for the compound topic sentence we considered a moment ago, consider the following thesis:
Example Thesis Statement
Efforts from NGO’s and the government to establish tidal hydro power in Nova Scotia face many obstacles, but by working together the two groups can meet with success by 2020.
Our compound topic sentence establishes the connection to the parts of this thesis by specifically mentioning “the government” and “obstacles,” so that the reader knows what part of the thesis the associated paragraphs will explore, and by giving some further detail, so that the reader better understands what nuances of the paper will pick out.
As we saw with compound topic sentences, the topic sentence for a paragraph does not always need to relate directly to the thesis. For example, the topic sentences that follow a compound topic sentence refer to the compound topic sentence, but it refers to the thesis. Similarly, in longer essays that use subsections, topic sentences can refer to the main point laid out in the subsection’s introduction.
What’s important here is that the topic sentence either connects to the thesis or connects to something else, which in turn connects with the thesis.
Being the sentence that encapsulates the paragraph, a topic sentence often provides an ideal place to transition from the topic matter of the previous paragraph or section to the topic matter of the present paragraph or section. Transitioning is really an optional function of the topic sentence, but if the transition does not appear in the topic sentence, normally it should appear be just before the topic sentence.