Calvin Olsen, First-year Writing professor, academic editor, English tutor
You’ll hear a lot of different metaphors for what makes a good thesis (and you have already heard one or two from previous answers). For college writing, I find that the best one is to consider your thesis as a road map for your paper. Your reader wants to know where you’re going to end up in the end, or at least where you plan to go.
If you can inform them where you’re headed before the journey starts, they’ll already have their own ideas in mind. One of the best things about college writing is that your audience is generally well-informed. You’re not writing to people that have never read the idea/argument/text you’re talking about; instead, you’re writing to convince them that your ideas are the most correct. Chances are they have their own argument, so your thesis should simply set them up for where you will travel throughout the essay.
Setting up your thesis as a road map allows you and your reader to think of each paragraph as a stop along the way. If your thesis is “Frankenstein’s monster is not human because he is physically superior to the human race” your readers can narrow down possibilities for where you’ll go. They’ll have a general expectation for what evidence you will and provide. You don’t need a 100-word thesis that specifically tells the reader everything you’ll say in the paper—you just need to identify your argument and let the reader know where you plan to be in the end. Together with the rest of your introduction, your road map thesis will prepare your reader to know right where you're at and which direction you're headed.