Even though an invention or discovery is new and useful, it is not patentable unless it fits within one of the above listed statutory classes. Section 706.03(b) of the MPEP (Manual of Patent Examination Procedure) lists several examples of subject matter which is not patentable:

   a. Although an arrangement of printed matter in a form such as a book may appear to be an article of manufacture, it has been held not within the statutory classes;

   b. A substantially unaltered thing which occurs in nature, such as a deveined shrimp, is not an article of manufacture;

   c. A method of doing business such as an accounting procedure or advertising program has been held not in a patentable class;

   d. A scientific principle, law, or theorem, not associated with a tangible structure is not considered as being within the statutory classes.

Other ideas, inventions, or discoveries found not patentable include: abstract ideas, mental processes, and new properties of materials, compositions, or mechanisms. In recent years the courts, the PTO, inventors, and legislators have wrestled with the application of patent laws to computer programs. In most instances, algorithms, or listings of computer program language are currently not patentable unless associated with a particular piece of tangible hardware; but this is a constantly developing area of patent law.

Novelty

One of several requirements for patentability is that an invention be new or novel. This requirement is set out in 35 USC 102 and the application of the statute to a particular case may be very confusing.

The novelty test is the requirement that no invention may be patented if the same invention is already known in the United States or described in printed matter or patented anywhere else in the world. Even though an invention has not been patented in the U.S. it is not patentable if previously known or used by the public.

No patent may be granted on an invention patented or described in a publication anywhere more than one year prior to the date a U.S. patent application is filed or in public use or on sale in the U.S. more than one year before the date a U.S. patent application is filed. Many inventors have run afoul of this part of the novelty test. For example, an inventor who published a description of his invention in a technical journal and then delayed the filing of a patent application for 18 months would be denied a patent. An inventor who sold prototypes of her invention at a trade show might also be denied a patent if she waited more than a year before filing a patent application.

Although the novelty test has prevented many inventions, it is relatively easy to avoid. Nearly any difference between the claimed invention and the previously known invention (prior art in patent jargon) is sufficient to avoid rejection based upon the novelty test. The difference between the prior art and the invention may be insubstantial, but it must still be a variation recognizable under the patent laws. The difference must be in the concept or the operation of the invention rather than its physical manifestation.

Unobviousness

Unobviousness is the third test of patentability and is many times more often a bar to patentability than either novelty or failure to come within a statutory class. ("Nonobviousness" is sometimes used as an equally clumsy alternative to unobviousness.) Section 102 of 35 USC provides that in addition to novelty an invention must not be one in which the differences or improvements would not have been obvious to a person having "ordinary skill" in the area. Even though an invention is novel, a patent will be refused if the subject matter of the invention would be obvious to a person knowledgeable in the area of the invention.

This test is nearly always the most important to any inventor and also the most subjective and difficult to apply. In a case known as Graham v. John Deere Co., 383 U.S. 1, 17-18 (1966) the U.S. Supreme Court set out some not terribly helpful steps for determining unobviousness:

   a. Establish and evaluate the prior art;

   b. Perform the novelty test;

   c. Establish the level of skill of persons knowledgeable in the area of the art at the time of the invention;

   d. Use a, b, and c above to determine the obviousness or unobviousness of the invention.

Although not adding much to the definition of unobviousness; the court did indicate that secondary, more objective factors, including commercial success, long-felt but unmet need, and failure of others to fill the need could be used in determining whether the test was met. If an inventor can show that his invention is commercially successful or solves a known problem that other have failed to solve, he is much more likely to be able to prove his invention is unobvious.

Although it is not strictly a legal precedent since the Graham case, many patent practitioners still use a phrase from a previous case to help determine unobviousness. That is, an invention is unobvious if it produces "unusual and surprising results."