A thesis statement is a sentence that states what you want your paper to show, what you want to convince your readers after having read your thesis.
This is the foundation of the entire work and informs the reader exactly what you wish to achieve with the paper, what you wish to prove or disprove.
Unless you are documenting research or writing a purely descriptive essay, you will be basing the paper around this thesis statement, so it needs to be well thought out and described.
What is a Thesis Statement Good For?
If an assignment asks you analyze, argue, compare and contrast, establish a cause or otherwise interpret, the chances are that you will need to base it around a clearly defined thesis statement.
This sets out your position, and every part of the paper will need to refer to back to it in some way.
The Four Step Plan to Writing a Good Thesis Statement
Assertive: Your thesis statement must state exactly what you intend to prove with the paper.
Singular: The thesis statement, in most cases, should contain only one idea, keeping the paper focused.
Specificity: The thesis statement should be as specific as possible, whilst making your stance clear. One sentence is enough for shorter papers.
Position: It should be in the introduction, in most cases at the very end.
Tell the Reader What You Intend to Prove
Knowing what you are trying to achieve, and committing it to paper, can often be the difficult part, and writing the actual statement can be one of the most daunting aspects of the essay. You are trying to make sure that it informs the reader of exactly what you are proposing.
A thesis is not the subject of the paper but an interpretation or point of view.
For example, you may be writing a paper about the effects of adding omega-3 fatty acid supplements to the diet. That is the subject of the paper.
The thesis would set out what you believe, for example, you may decide to argue the case that you believe that Omega 3 fatty acids supplements are beneficial to health. You could equally argue that they have no effect, or that they are harmful.
One Paper = One Concept
For most papers, you want to discuss one concept and elaborate upon that, otherwise the paper quickly loses direction, never answering a point and thoroughly confusing the reader.
For example, you may have decided to write a paper about gambling addiction. Trying to write a paper stating that both Pavlovian and Skinner's conditioning influence behavior is difficult.
It is better to pick one of the two types and base an essay around that. You could argue that operant conditioning is the major factor underlying the addiction, and set out to prove it. Pavlov would still crop up in the paper, but as part of the background.
Drawing Things Together
Your thesis statement should draw together all of the background contained in your introduction and turn it into a single statement. It is not a short rerun of the introduction, but a position.
Where Does the Thesis Statement Belong?
A thesis statement should be in the introduction of the paper, taking up a sentence or so. It is generally in the first paragraph, although some writers prefer to discuss the background and build up to the thesis at the end of the introduction.
This is generally perfectly acceptable, although you should check with your supervisor.
The Thesis Statement - Changeable
In a research paper, it is a little easier to write the thesis statement, because you already know your hypothesis, and will be basing it around that.
For an essay, you will need to establish your aim, and the overall direction of the paper. Just because the thesis statement is the foundation of the experiment does not mean that you need to do it first.
It is usually best to do some background information and skim through the sources before trying to fashion a statement. This will become your 'working' thesis and, unlike a hypothesis, it can change and adapt as you write and modify the paper.
A thesis statement is not set in stone, and can be modified and refined as you develop the essay. As you uncover more information, you may change your view slightly.
In an argumentative essay, for example, where you have to try to rebut arguments, it is not unknown for the writer to convince themselves that the opposite is true, and completely change the thesis. This is not a problem, and is all part of the scientific process.
Once you have written your essay, and are ready to proof-read, it is important to check your work and ensure that it addresses the thesis. Every single paragraph should be related to this initial statement in some way, or it risks drifting off into irrelevance.