a. A process: This class is usually a method of producing one of the three other classes of invention, such as, a method of making steel. The result of the process need not be a patentable item as long as the process is new or otherwise patentable;

   b. A machine: Machines are ordinarily easy to classify and include such common items as automobiles, wrenches, and cameras;

   c. A manufacture or article of manufacture: Articles such a rulers, bicycle seats, types of cloth or clothing, and video cassette cases are considered articles of manufacture. Ordinarily an article of manufacture does not primarily feature moving parts. Although it is sometimes difficult to determine whether an invention is an article of manufacture or a machine; this difficulty is usually not significant, because the inventor is not ordinarily required to elect a particular classification;

   d. Compositions of matter: Composition of matter inventions most commonly involve some chemical composition where the chemical composition is of more importance than the shape and includes all chemicals, gasoline additives, adhesives, and plastics. As with all the other classes things which occur in the same form in nature are usually not patentable;

   e. New and useful improvements: This classification is the most difficult to categorize and involves a new method or process for using a previously known invention in one of the four other classes. The use of a golf tee for picking teeth would be an example of using an old invention for a new purpose. The new use rather than the tee would be the subject of the invention. A new and improved golf tee, however, would be better classified as an article of manufacture than as a new and useful improvement. New use inventions are actually treated as process inventions under patent procedures.