Topic sentences play an essential role in any well-written term paper. The topic sentence states the main idea of the paragraph. It does for the paragraph what a thesis statement does for the term paper as a whole: it serves as the unifying theme. Topic sentences also show the relationship between the paragraph and the thesis statement. Usually placed at the beginning of a paragraph, good topic sentences help guide the reader through the thought process of your term paper. Because the topic sentence is supported by all subsequent sentences, topic sentences provide the additional benefit of keeping your writing on track.

The following paragraph from the term paper "The AIDS Emergency in Africa" shows a good topic sentence in action.

The magnitude of the global AIDS pandemic is reaching alarming new heights in the developing world. As of 2003, 42 million people have the HIV virus, and 29.4 million of them live in Africa. Yet, 99 percent of Africans who need life-extending anti-retroviral (ARV) medicines do not have access to them.

In the above paragraph, you will notice that the topic sentence is the most general. Like a good news headline, it provides the reader with the main idea at a glance. The sentences that follow it supply statistical evidence to support the topic sentence. The topic sentence relates the paragraph to the term paper's thesis: that the nations of the world should help fund AIDS relief in Africa.

Though topic sentences often appear at the beginning of a paragraph, it is sometimes better to place them in the middle or at the end. While all of your paragraphs should relate back to the term paper's thesis in some way, they won't all relate to each other. Beginning with a transitional sentence and saving the topic sentence for later can help a reader follow your train of thought more easily. When concluding an term paper, it may be more effective to start with specifics and end by summarizing the main idea.

Not every paragraph requires a topic sentence. If one of your topics is supported by much more evidence than the others, it may make sense to break it up into two or more paragraphs to give your term paper balance. Instead of repeating a topic sentence, you can demonstrate that you are continuing the thought with a phrase like "in addition" or "furthermore." In some paragraphs the topic will be obvious, making the topic sentence redundant.

Here is a quick checklist for writing effective topic sentences:

- The topic sentence states the main idea of the paragraph.
- The topic sentence shows the relationship between paragraph and thesis.
- The topic sentence is the most general sentence in paragraph.
- The topic sentence is supported by details in subsequent sentences.