Thesis Sentence Definition

What's the Big Idea?Remember that an essay is a piece of writing that attempts to explain something, analyze something, or present the author’s insight. An essay’s purpose is to provide a written explanation of your own ideas, interpretations, and evaluations—your direct reflection on, or analysis of, a focused topic.

In order to provide insight, analysis, and/or interpretation, an essay needs a focus. An essay’s focus occurs in a thesis sentence, a sentence that provides the author’s main idea or argument in succinct form.

Most college essays will require a thesis sentence, a sentence in which you make a claim or proposition that you then support with evidence and examples, in order to prove the validity of that claim.  The thesis, which often comes toward the start of an essay, is the key idea of the whole essay, encapsulated in one sentence.

When you’re asked to write an “essay” as a course assignment, most likely you will be asked to write a thesis-support essay.

Thesis-support essays are just what their name implies. They offer a thesis near the start of the essay, usually at the end of the introductory paragraph, and then follow with supporting ideas and information. Usually, each unit of support starts with a topic sentence which extracts an idea from the thesis and makes a point about that part of the thesis idea.

Here’s a way to visualize a basic thesis-support essay:

diagram of thesis-support essay showing 5 consecutive parts: 1. Thesis, 2. Topic Sentence 1 with details, 3. Topic Sentence 2 with details, 4 Topic Sentence 3 with details, and 5 Conclusion Thesis

Writing a good thesis sentence is key to academic essay writing, as it captures the essence of the writer’s insight. The rest of the essay can then develop from, elaborate on, and offer evidence for the thesis sentence’s idea. In other words, the thesis sentence makes a promise, or sets up an expectation, for the type of information to follow in the essay.

View the following videos for definitions and examples of thesis sentences.

The first video deconstructs three thesis statements to show the topic, claim, and detailed points of each.

Note: Some content in the video “Writing an Effective Thesis Statement” is presented visually. You may listen to this video with audio description.