Topic Sentences

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.

Where should the topic sentence be placed within a paragraph?

Your instructor may have guidelines for you about where to place topic sentences. If it is up to you, the topic sentence may appear:

  • At the beginning. In many writing situations, the author places the topic sentence at the beginning of the paragraph. Readers often expect cues related to the paragraph’s focus, claim, and main idea. In this position, the topic sentence makes an initial point and the remainder of the paragraph provides relevant supporting details.
  • In the middle. In a few writing situations, the author may use the first sentence (or two) in a paragraph to act as a transition between paragraphs. The topic sentence that follows the transitional sentence(s) summarizes the paragraph’s main idea and helps provide unity to its content. In this position, the topic sentence links the supporting details presented before and after it.
  • At the end.In some writing situations, the author may place the topic sentence at the end of the paragraph. Groundwork laid at the beginning of the paragraph can be built upon until it culminates at the end. Or, in a long or complex paragraph, the author may choose to restate the topic sentence in the form of a concluding sentence to remind the reader of the paragraph’s main point.

When might a topic sentence be unnecessary?

If they are not required by an instructor, there are a few instances when a topic sentence might be unnecessary, including when:

  • The train of thought continues from the previous paragraph. Writers may find they have a lot to say about a sub-point in their essay and the number of supporting details could result in unwieldy paragraph length. When a previously developed idea spills into a new paragraph, a topic sentence may not be needed for the resulting new paragraph.
  • The paragraph narrates a series of events. Writers may become narrators in some settings; hence, this transmission of events or experiences may speak for itself and a topic sentence could get in the way.
  • The main idea of the paragraph is obviousWriters may sometimes present reliable, convincing evidence in such a way that the point of the paragraph is obvious and a topic sentence becomes unnecessary.

When during writing should the topic sentence be identified?

Because writing is a thoughtful, constructive process, writers may not always know what form their thoughts will take until they make it onto the page. This process involves a developmental progression that usually includes several drafts. Writers may identify topic sentences at different points during the writing process. Sometimes writers know right away what the topic sentence looks like and where it fits within the paragraph. Other times, they need to look at earlier drafts and analyze the main point of the paragraph. Then, a decision can be reached whether or not a topic sentence is necessary and, if so, where it should be placed.

How do I write or revise a topic sentence?

When writing or revising a topic sentence, consider whether the topic sentence:

  • concisely summarizes the main idea or purpose of the paragraph?
  • effectively guides the organization of the paragraph’s ideas?
  • clearly announces the direction of the paragraph’s conversation?
  • actively supports the relationship between the paragraph’s ideas and the essay’s thesis statement?
  • adequately prepares the way for the content of the paragraph?
  • firmly establishes boundaries for the supporting details and evidence presented in the paragraph?