Once you have determined your specific purpose (to convince your audience that smoking is harmful), you probably feel that you have narrowed your topic sufficiently to begin gathering information. You begin an online search using some of the key words from your specific purpose (for instance, the harmful effects of smoking) and you are amazed to find that those few key words yield hundreds of possible results -lung cancer, throat and tongue cancer, emphysema, hardening of the arteries, accelerated aging, pulmonary disease, and the list goes on and on. You know you can’t possibly discuss all of these effects in a four- to five-minute speech, so what now? Now you need to become selective. Which of those results most interests you? Which might best persuade your audience to quit smoking? You narrow your topic further and decide to concentrate solely on the research involving lung cancer. But which points about lung cancer do you want to share in your presentation? You need a thesis statement -one sentence that pulls all of your information together and informs your audience of the major points that you intend to cover during your speech. A thesis statement for a speech on lung cancer might choose to examine the link between lung cancer and smoking, the treatment options for lung cancer patients, and the mortality rate for this type of cancer.
A thesis statement provides your audience with a “preview ” of your speech in much the same way that a movie trailer previews an upcoming new movie. Movie trailers reveal enough about the movie to capture the audience’s attention and to gain their interest; an effective movie trailer shows us just enough to make us want to see the movie. You want your thesis to do the same. An effective thesis lets your audience know what ideas you’ll cover, what you consider most important, and how many details you’ll include. The movie trailer certainly doesn’t reveal the ending or show you the entire movie. Your thesis, likewise, doesn’t go into great detail. You don’t give all your facts, tell all your stories, or share all of your examples in your introduction; you share that information gradually as you work your way through the speech. Your thesis, then, is simply an overview -or a preview -of what your audience will hear if they continue to pay attention and listen to all of your presentation.