Whenever you are writing to explain something to your reader or to persuade your reader to agree with your opinion, there should be one complete sentence that expresses the main idea of your paper. That sentence is often called the thesis, or thesis statement. (Some other names it goes by are "the main idea" and "the controlling idea.") Based on everything you've read, and thought, and brainstormed, the thesis is not just your topic, but what you're saying about your topic. Another way to look at it is, once you've come up with the central question, or organizing question, of your essay, the thesis is an answer to that question. Remember, though, while you are still writing your paper, to consider what you have to be a "working thesis," one that may still be "adjusted." As you continue to write, read, and think about your topic, see if your working thesis still represents your opinion.
Handy reminders about the thesis:
The thesis usually comes within the introductory paragraph, which prepares the reader to listen to your ideas, and before the body of the paper, which develops the thesis with reasons, explanations, and evidence or examples. In fact, if you examine a well-written thesis, you will find hidden in it the questions your reader will expect you to answer in the body. For example, if your thesis is "Cannibalism, if practiced tastefully, can be acceptable in extreme circumstances," the body of your essay will develop this idea by explaining HOW it can be practiced tastefully, WHY it would be acceptable, and WHAT you would consider extreme circumstances.
Make sure your thesis is in the form of a statement, not a question. "Can we save the Amazon rain forest?" is an ear-catching question that might be useful in the introduction, but it doesn't express an opinion or perspective as the following statements do:
Make sure your thesis expresses your true opinion and not an exaggerated version of it. Don't say "Computers are wonderful" or "Computers are terrible" if what you really believe is "Computers do more good than harm" or "Computers do more harm than good." Why commit yourself to an extreme opinion that you don't really believe in, and then look like you're contradicting yourself later on?
Make sure your thesis covers exactly the topic you want to talk about, no more and no less. "Drugs should not be legalized" is too large a thesis if all you want to talk about is marijuana. "Boxing should be outlawed" is too small a thesis if you also want to discuss wrestling and football. Bite off as much as you can chew thoroughly--then chew it!
Shape your thesis to fit the question you wish to answer. A thesis can come in many forms, including the following: