Remember that a thesis is a single sentence that expresses the controlling idea of a written work. In other words, the thesis is the core of the essay. It guides the goals and structure of the work by letting the reader know what the writer will be discussing in the body paragraphs, and in what order.
Also remember that there is a significant difference between a thesis and a topic. A topic is the broad subject of a written work, and can include multiple thesis statements. The thesis is a focused point or argument about something within the topic.
Suppose you were assigned the topic of pet ownership. You wouldn't be able to write an essay based on that topic— it's too broad. First, you must decide which aspect of pet ownership you want to write about or communicate to readers. You might, for example, make the following statement:
Although many people assume that owning a pet is easy, it actually comes with a great deal of responsibility, such as grooming, feeding, and training.
Here's another option:
Due to their companionship, understanding nature, and ability to help during emergencies, pets can fit the definition of lifesavers.
As you can see, these two thesis statements are very different, and are only related through their very broad shared topic of pet ownership.
Once you've selected a topic and a thesis, you must support the thesis by developing your ideas effectively. This is accomplished through a process of clearly articulating your ideas and supporting them with evidence and reasoning throughout the essay.
So, when writers refer to development, they're not only referring to development of the essay as a whole, but also to the process that takes place at the paragraph level. Paragraphs function like mini-essays: Each of them contains their own main ideas, topic sentences, and support.
To effectively state and support a thesis, most essays must also promote related points— points that, together, prove or support the thesis. Recall that, in writing, these are called main ideas. A main idea is a point or concept that drives one or more body paragraphs of an essay. Each main idea in an essay should contribute to, or support, the thesis statement in some way.
A claim is a type of main idea in which the writer makes a statement that must be defended. A claim is an assertion made by the writer. The thesis statement is thus the primary claim of the essay— the object of all of the essay's support, ideas, and evidence.
A main idea, when coupled with a claim, is usually the controlling idea of the paragraph. When working on the level of the paragraph, the main idea and the controlling idea are synonymous.
The thesis statement is the main point of the essay, so it needs support in order to hold up. Support refers to any evidence, logic, or other technique (e.g., clarification, expansion of ideas) that bolsters an essay's claims. The purpose of support isn't only to prove that a thesis is true, but also to explain or strengthen the essay's main ideas.
Evidence is one of the most common forms of support. It is proof of the validity of a claim or claims, and can include the following:
Because essays consist of paragraphs that use forms of support to back up the thesis, it's important to consider paragraphs in order to understand the essay as a whole. As mentioned above, paragraphs are like miniature essays that include a topic sentence (i.e., the sentence that states the paragraph's thesis) and support— usually evidence for the topic sentence.
Following are paragraphs from the same essay which demonstrate how an overall thesis might be introduced, developed, and supported. This first paragraph serves as the essay's introduction:
When you think about your goofy pet dog, your lazy house cat, or even your loud pet parrot, you might not consider that they could save your life. Mounting evidence suggests that pets are more than a playful mess to clean up after; they are key to a happy, healthy life. Due to their companionship, understanding nature, and ability to help during emergencies, pets can fit the definition of lifesavers.
The thesis appears as the last sentence of the paragraph: "Due to their companionship, understanding nature, and ability to help during emergencies, pets can fit the definition of lifesavers."
Because of this thesis, we know that the main point and narrowed-down topic of the essay is that pets are lifesavers, and we know that the main ideas related to that point are companionship, an understanding nature, and ability to help during emergencies. That helps us to figure out what kind of evidence and support may be included in this essay: Perhaps the essay will use data about the health benefits of owning a pet, perhaps it will discuss research from others who have investigated this topic, or perhaps it will include descriptions of personal experience.
Now consider this next paragraph, keeping the essay's thesis in mind as you do:
The companionship of pets offers health benefits, demonstrating the lifesaving qualities of pets. There all kinds of pets that individuals or families can adopt. Some of the most traditional pets are dogs, cats, birds, rodents (such as hamsters and guinea pigs), and fish. Less common pets include rabbits, small pigs, raccoons, and snakes and other reptiles. Exotic animals might also make excellent pets, but may require a special permit and special care. There is an ideal type of pet for each individual or family.
The topic sentence of this is paragraph is "The companionship of pets offers health benefits, demonstrating the lifesaving qualities of pets," which means that the support in this paragraph should focus on the main idea of companionship mentioned in the thesis. So is the support here effective for the main idea of the paragraph and the essay's thesis?
No, it is not. All of the sentences that come after the topic sentence are discussing different types of pets that individuals and families can adopt. The author gives examples of different types of pets, and simply states that there is an ideal pet for each individual or family. Even though this information is related to the broader topic of pet ownership, it does not belong in this essay. It does not support the idea that the companionship of pets offers health benefits (the main idea of this paragraph) and it does not support the overall claim of the thesis (that pets fit the definition of lifesavers) because it does not address pets' companionship, understanding nature, or ability to help during emergencies.
In order to better support the topic sentence "The companionship of pets offers health benefits, demonstrating the lifesaving qualities of pets," and to therefore better support the thesis, here is a revised version of this paragraph:
The companionship of pets offers health benefits, demonstrating the lifesaving qualities of pets. Both mental and physical health can improve when owning a pet. Petting or caring for a dog or cat lowers levels of stress and combats loneliness. Dog owners in particular may find themselves socializing more often when taking their dog for walks and to dog parks. In addition, walking a dog can lower blood pressure and decrease the risk of heart disease (Fields 2013). By improving the health of their owners through companionship, pets improve - and even save - these owners' lives.
In this version of the paragraph, the support provided directly relates to both the topic sentence and thesis. There are facts, such as that petting or caring for a dog or cat lowers levels of stress and combats loneliness, dog owners socialize more, and walking a dog can lower blood pressure and decrease the risk of heart disease. These facts help to support the idea that the companionship offered by pets comes with health benefits.
Additionally, the support in this paragraph supports the thesis, which lists companionship as one of its main ideas.