Topic Sentences

Learning Objectives

  • Identify topic sentences in paragraphs

Topic Sentences

Key Takeaways

In academic writing, a topic sentence is a sentence that clearly expresses the main idea of a paragraph. It guides the reader by summarizing what the paragraph will discuss and how it connects to the overall argument or purpose of the writing.

A strong topic sentence serves two key functions:

  1. States the Main Idea: It presents the primary point that the rest of the paragraph will support with evidence, examples, or analysis.
  2. Provides a Transition: It connects the paragraph to the previous one, helping the reader follow the logical flow of the argument.

By clearly establishing both the focus and connection to the larger text, topic sentences help maintain clarity and organization in your writing.

Some instructors refer to it as a key sentence because it highlights the central point of the paragraph, though it may not always directly announce the topic or be limited to one sentence.

Example: Strong Topic Sentences

Consider these two examples of topic sentences about epidemiological and etiological evidence. If you are unfamiliar with these terms, epidemiological evidence is related to the study of diseases. Etiological studies refer to the study of the origin of a disease.

  • Version A: Now we turn to the epidemiological evidence.
  • Version B: If the evidence from studies on the cause of the disease (etiology) supports the hypothesis, the evidence from studies on how the disease spreads (epidemiology) is also compelling.

Both versions introduce the topic of epidemiological evidence, but they serve different purposes.

  • Version A simply announces the topic without explaining its importance or how it connects to previous ideas.
  • Version B not only introduces the topic but also explains why it matters. It shows that the new evidence (epidemiology) supports the earlier discussion about the cause of the disease (etiology), building a stronger argument.

This makes Version B clearer and more useful because it connects the new paragraph to the one before it, helping the reader understand how the ideas are related.

Try It: Topic sentences

Read the paragraph about camera flash technology and answer the question below:

When a camera flash is used in a low-light environment, the subject’s eyes may appear red in the finished photograph. What is known as “red-eye” is the result of light from the flash reflecting off the pupils of the eyes. The phenomenon of red-eye can be lessened by using the red-eye reduction feature found on many SLR cameras. This feature activates a lamp that shines a small light directly into the subject’s eyes. When this happens, the diameter of the pupil is reduced, thus tightening the opening in the iris. Since a smaller pupil means a smaller host for the reflection, the chances of red-eye occurring are greatly reduced.

How Topic Sentences Relate to Thesis Statements

Topic sentences have a topic and an angle or claim, just like thesis sentences. But the angle of topic sentences usually is smaller in range than that of the thesis sentence. Very often the topic remains the same from thesis to topic sentence, while the angle shifts as the writer brings in various types of ideas and research to support the angle in the thesis.

Example: TOpic Sentences from Thesis statements

Look at this sample below; these are topic sentences created from the thesis sentence. The topic remains the same in all (regular exercise) and the overall angle remains the same (benefits). But the angle narrows and shifts slightly from topic sentence to topic sentence as the writer brings in different supporting ideas and research.

Thesis Sentence Topic Angle
A regular exercise regime creates multiple benefits, both physical and emotional. Regular exercise Physical and emotional benefits
Topic Sentence Topic Angle
One physical benefit of having a regular exercise regime is longevity. Recent studies have shown that… Regular exercise Physical benefit of longevity
Exercise reduces heart and cholesterol rates when done at least three times per week… Regular exercise Physical benefit of reduced cholesterol
Another physical benefit of regular exercise is that it results in a stronger heart and lungs… Regular exercise Physical benefit of stronger heart and lungs
People who exercise regularly have less trouble with sleep disorders… Regular exercise Physical benefit of less trouble sleeping
A benefit that spans the physical and emotional results of regular exercise is the release of endorphins, or substances produced by glands as a byproduct of exercise… Regular exercise Physical and emotional benefits of endorphins
In multiple studies, regular exercise has been shown to reduce stress… Regular exercise Emotional benefit of reduced stress
Because regular exercise often helps to slow the effects of aging and maintain a good body weight, people who exercise regularly experience the emotional benefits of good self-image and self-confidence in their looks… Regular exercise Emotional benefit of better self-image & confidence

Notice that in the examples above, the topic sentence reflects back to the overall thesis (A regular exercise regime creates multiple benefits, both physical and emotional.) and introduces the reader to the specific topic and angle of each paragraph (improving sleep, reducing stress, etc.).

Sometimes, you may need multiple paragraphs to help work your way behind the ideas related to one topic sentence because you have a lot of supporting information. An effective topic sentence not only introduces the topic of each paragraph, but it reminds the reader of the overall thesis, driving home the point of the piece of writing.

Watch It

Effective annotating includes taking careful notes to extract the main ideas from a reading. In order to find the main ideas, you’ll need to know how to identify the thesis statement and topic sentences in each paragraph. This video will walk you through that process, and also highlight some other key components of essays, like supporting details and transitional words and phrases.

You can view the transcript for “Annotating an Essay or Book” here (opens in new window).

In our next section, we’ll move beyond the topic sentence to all the other pieces that make up a strong paragraph, like supporting details and transitional words and phrases.