A thesis statement is the intellectual center of a paper. It offers a controlling generalization which informs your audience of the main idea that the paper will develop. A thesis is also a statement of intention, an assertion about your topic. It lets the reader know the topic you will deal with, it may impose limits on that topic, and it may suggest something of the paper's later development.
 

Statement of Fact	Revised Thesis
Many Anericans are buying foreign cars.	Many Americans are buying the Volkswagen Rabbit because of its low price, fuel economy, and high resale value.
London is an interesting place to live.	Cultural opportunities--particularly theaters, art galleries, and museums--make London an interesting place to live.
Inflation is one of the nation's major problems.	The nation's current inflation has had a serious effect on the housing industry.  Because many people are no longer able to afford to buy single-family houses, builders are going bankrupt and consumers are forced into renting apartments--often at very high rates.

An exact thesis statement gives a paper unity, precision, and emphasis. Unity means that all the elements stand in support of the topic as indicated by the thesis. It allows the writer to concentrate on the development of a specific topic and enables the reader to follow the progression of ideas.

An exact thesis also lends precision to a paper. Precision is exactness, the quality of avoiding ambiguity and vagueness.