The patent examiner at the U.S. Patent and Trademark Office (USPTO) requires that all three types of patents satisfy the novelty and unobviousness requirements.
Novelty is the easiest test to satisfy because all an applicant has to do is show that the invention is different than any existing patents. Slight differences in physical composition or process can allow an invention to pass this test.
Unobviousness is the harder test because the applicant must show that the invention would not have been developed from existing patented inventions. This means that a patented invention would not have been developed and changed to be the same as the applicant’s invention. In other words, the new invention must be so unique that a patent examiner could reasonably say that an old patented invention would not have been developed by a person skilled in the art (area of the applicant’s invention).
Another hurdle is the examiner can mix and match existing patented inventions to test the uniqueness of the new invention. This is a difficult test to pass and takes crafty and creative persuasive arguments to convince a patent examiner.
Mental processes which can be performed with only one’s mind or body cannot be protected by patents. Some type of hardware must be involved in the process to qualify for protection. The law does not want to limit what a person can do essentially with the body alone.
Utility patents are the most common patents and protect inventions that function in a specific and unique way that produces a utilitarian result. Examples are computer hardware, chemical structures, keyboards, automobile engines, and medical procedures.
Design patents protects a unique visible and aesthetic shape or design of an object. Examples are drawings of a computer monitor prototype, radio, phones, and shoes. However, the shape must be purely ornamental or aesthetic and not utilitarian. If the shape serves both an ornamental and utilitarian function, then a utility patent must be filed. A helpful way to distinguish between a design patent and a utility patent is to ask, "Is the novel feature there for only ornamental reasons, or for structural and functional reasons." If the answer is both structural and functional, then a utility patent must be filed.
Plant patents protect asexually or sexually reproductive plants like grasses, flowers, trees, bushes, and mosses.