A topic sentence is usually the first sentence of a body paragraph, and it expresses the main idea of that paragraph while also supporting the thesis of the entire essay. To achieve its purpose, a topic sentence should
have a clear connection back to the thesis; in other words, the reader should understand how it supports the entire essay's point.
be specific and narrow enough to tackle its idea well in one paragraph.
match the purpose of the paragraph through how it is phrased. For example, if its paragraph is informative, the topic sentence should state a fact, but if its paragraph is argumentative, the topic sentence should make a persuasive claim.
encapsulate the content of its paragraph in a single sentence -- anything in its paragraph that does not fit with its idea should be removed, or the topic sentence should be revised.
begin with a transition of some kind that links it to the idea the previous paragraph ended with. That way, the reader can see how the two ideas connect.
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