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What is a topic sentence?

A topic sentence summarizes the main idea or the purpose of a paragraph. In an essay, topic sentences serve an organizational purpose similar to a thesis statement but on a smaller scale; a topic sentence helps guide the organization of a single paragraph while a thesis statement guides the organization of the entire essay. A topic sentence may be placed at the beginning, middle, or end of a paragraph depending upon the way the writer chooses to organize the paragraph.

What are the functions of a topic sentence?

A topic sentence functions in several important ways:

  • It informs the reader of the paragraph’s direction

The topic sentence announces the direction of the paragraph’s conversation. With the help of an effective topic sentence, readers will better understand what the paragraph will be about.

  • It guides the reader through the major points that support the thesis statement

Since each paragraph—or a group of paragraphs—elaborates on a part of the thesis statement, a topic sentence can help clarify the relationship between the paragraph and the thesis statement. Clearly worded topic sentences may help readers find the paper’s position or argument more convincing.

  • It places boundaries on the paragraph’s content

The body of the paragraph provides support for the topic sentence. The paragraph should only include evidence and details that relate directly to the boundary established by the topic sentence.

Let’s look at an example:

Topic sentence: Specially trained dogs provide valuable services for various law enforcement agencies.

Details within the paragraph:

  • Drug Enforcement Administration officers use dogs to find various types of drugs.
  • Some dogs are trained to search for and locate bombs and other weapons for the Bureau of Alcohol, Tobacco and Firearms.
  • Police dogs can be used to track missing people or fugitives.
  • Cadaver dogs are trained to ignore the scent of live humans and search for human remains.

When the topic sentence prefaces the sentences with supporting details, the purpose of the paragraph is clearer to the reader. Together, the topic sentence and the body sentences create a well-organized and easy to follow paragraph:

Specially trained dogs provide valuable services for various law enforcement agencies. The Drug Enforcement Administration trains dogs to find even trace amounts of various types of illegal substances. The Bureau of Alcohol, Tobacco, and Firearms uses dogs to search for and locate bombs and other weapons, especially at large public events or arenas. Additionally, several local and federal agencies use dogs to track missing people or fugitives who may be found in a specific, localized area. Cadaver dogs, similarly, are trained to ignore the scent of live humans and search for human remains. These dogs are valuable assets to our country’s law enforcement organizations.