Chapter six discusses the requirement of utility, which is sometimes called usefulness. Showing utility is not an issue for the great majority of patent applications. After all, why would an applicant spend thousands of dollars to secure the exclusive right to something useless? Instead, the requirement is most often used by the Patent Office to screen out clearly unworkable devices such as alleged perpetual motion machines. Nonetheless, it is important for an application to disclose at least one useful aspect of the claimed invention.