A good thesis statement controls the overall writing objective of a book or research paper. Thesis statements are applied to analytical, expository and argumentative writing.
Sometimes called a thesis argument, a well-written thesis statement presents a claim that is a supported throughout a book or paper with concrete examples. An analytical thesis statement is supported by evidence that breaks down and evaluates an issue. An expository thesis statement is supported by evidence that explains an issue. Argumentative thesis statements are supported by evidence that backs up opinions, proposals or causal-analysis evaluations. Thesis statements are typically used to keep a book's persuasive goals on target, and writers sometimes need to revise their statements as goals change.
Argumentative thesis statements are usually controversial in nature, especially if the writer has tapped into a hot issue. Controversial claims are beneficial in that they give a book or paper forward momentum, exploiting what many composition instructors call the "so what" of the thesis. The "so what" of a thesis statement considers whether or not an argument is worth pursuing and begs feedback from an opposing side. Purdue University's online writing center provides this example: "High school graduates should be required to take a year off to pursue community service projects."