An essay’s thesis or thesis statement is its central or controlling idea, its essence, its main idea. It is the focal point for your topic. It is usually expressed as an opinion or an assertion, usually in a single sentence, which the rest of the essay supports and augments. It is typically the last sentence of the opening paragraph (when you are using paragraphs in a longer essay), though it can also be effectively placed elsewhere.

If, for example, your topic is on the search for life on other planets, your thesis, among the many possibilities, might be:

• Recent research into the topography of Mars increases the odds that Earth is not the only planet in our solar system that harbours life.
• While the search for extraterrestrial intelligence is an important function of the SETI Institute, the Institute also provides resources for students and educators in all aspects of astronomy and keeps the public informed about current issues in the field.
• Among the scores of movies about extraterrestrial intelligence, Arrival and Close Encounters of the Third Kind are the most thought-provoking.
• The Drake Equation provides no hard evidence of the existence of intelligent life elsewhere in the universe, but it does suggest that the odds are in its favour.
• No official government investigation or serious scientific study has confirmed the existence of UFOs.

A good essay will develop the thesis in a series of paragraphs that provide some combination of examples, details, definitions, anecdotes, comparisons, contrasts, causes, and effects so that readers feel satisfied that the writer has established the validity of the thesis.

Keep in mind that your thesis might evolve and change as you work your way through the process of composing your essay. While revising your first or second draft, you may realize that some of the content of your essay does not quite relate to your thesis, which you may then have to refine.

A Blueprint Thesis

A blueprint thesis provides readers with not only the essay’s controlling idea, but also the reasons and arguments in phrase or even word form in support of the controlling idea. A simple blueprint thesis for a short essay about the popularity of jeans might be:

Jeans are so popular because they are comfortable, durable, and stylish.

For a longer essay, the thesis would add more supporting points:

Jeans are so popular because they are an icon of our culture, cleverly marketed, comfortable, stylish, and durable.

The advantage of the blueprint thesis is that it alerts the reader to the essay’s organizational pattern and so enhances the overall clarity of the text.  One disadvantage is that it could reduce readers’ interest in the rest of the essay since it gives much away. Another disadvantage is that the more complex the reasons in support of the thesis are, the more difficult the essay becomes to construct.

A General Thesis

A general thesis presents little else than the essay’s controlling idea:

• There are several reasons why jeans are so ubiquitous an article of clothing.
• It is not difficult to explain the universal appeal of jeans.

The advantage of the general thesis is that it is concise and to the point. The disadvantage is that it can seem too much a statement of the obvious.

A Question Thesis

A question thesis poses a question to which the rest of the essay responds.

Why are denim jeans so popular?

An Implied Thesis

The implied thesis is not in a single sentence in an opening paragraph. Rather, it floats between the sentences, an authoritative but invisible presence. Here is an example:

Wander around a shopping mall, an airport, or a college campus, observe what the people are wearing, and you will learn, if you did not know already, that denim jeans are among the most popular items of clothing that people choose to wear. Today, in my college English class, 14 of the 26 students—and my professor—are wearing jeans. The average North American college student owns seven pairs of jeans (Ellison 14).  Once acceptable only in casual venues, jeans are common now in the workplace—my bank manager wears jeans on casual Fridays!—and in restaurants that once had jacket-and-tie dress codes.

We love jeans because…

There is no single sentence that spells out the thesis, but its presence is there, confirmed by the opening phrase of the second paragraph.

The implied thesis is common in the writing of professional journalists and academics. In a good essay or article, readers know what the thesis is by the time they have come to the end of the introduction, but there may not be a single sentence they can underline and write beside in the margin “thesis.” For students, the implied thesis is a bit of a risk: many teachers want a clear thesis, as an obvious sign that the student, whose essay they are evaluating, has learned and can apply this essential feature of academic writing.

An Argumentative Thesis

The thesis for an argument essay needs to be especially forthright. It must signal clearly to your readers your position on the issue under consideration.

An oil pipeline, spanning two provinces, would threaten the environment, fail to create enough jobs to justify the government’s investment, and delay the crucial search for renewable sources of energy.