When you write for academic audiences, you'll generally be expected to write with a sense of purpose. Often, your teachers will say that they expect you to have a "clear thesis statement" in your papers. But what does that mean?
In persuasive writing, a thesis statement should communicate your position, solution, or interpretation to your audience. It should be clear, specific, and interesting to the audience. You can think of a good thesis statement as having four key elements:
A clear stance. Is the claim debatable? Is there a contestable position? Are there ways that the tension of the thesis could be made more clear?
A manageable scope. Is the thesis narrow enough that it can be covered within the assignment requirements? Has the writer adequately focused the topic?
Genuine stakes. Who might care about this topic? Who is the writer addressing? Does this statement generate an interest in the reader? Does the thesis indicate how the writer is moving beyond the obvious?
A sense of logic. Does the thesis explicitly or implicitly lay out a framework for the argument? Does the thesis indicate the logical "pieces" that must fit together in order to reach a persuasive conclusion?
Another way of thinking about your purpose for writing is to determine your exigency. Lloyd Bitzer defines an exigency as "an imperfection marked by urgency; it is a defect, an obstacle, something waiting to be done, a thing which is other than it should be." In other words, you can think of your writing as an attempt to address an urgent imperfection. Your writing will often be much more powerful if your audience understands why you're writing--in other words, if they understand the exigency of your work.