The following article appears in the journal JOM, 43 (6) (1991), p. 45. JOM is a publication of The Minerals, Metals & Materials Society

Considering What Constitutes Prior Art in the United States

In analyzing an existing patent or in deciding whether to file a patent application for an invention, it is almost always necessary to consider the "prior art." Prior art may be defined very broadly as the entire body of knowledge from the beginning of time to the present. For example, in a U.S. Supreme Court case more than 50 years ago, the work of Benvenuto Cellini, the noted Italian artist who died in 1571, was cited in the judicial opinion as part of the prior art, invalidating a patent for the lost-wax casting of jewelry. That case was an extreme one, however, and does not give a fair indication of how prior art is considered.

Under U.S. patent laws, defining what prior art is pertinent is often critical. The patent statutes define what constitutes prior art for purposes of anticipating an invention or the claims of a patent application or patent. Unless the alleged prior art can be brought within one of the definitions set forth in the statutes, it is not pertinent and will not be considered.

It is interesting to note that no one has developed a satisfactory statement of what constitutes an invention. Philosophically, this seems to follow from the fact that an invention is something which is found by reaching out into the unknown. Since an invention cannot be defined by describing something which is still unknown, the only alternative is to state what is not an invention. This is done in the patent law by defining what is in the prior art.

The prior art is defined by Title 35, United States Code, Section 102, which states: "A person shall be entitled to a patent unless...." This language is followed by a series of definitions, the most important of which are summarized in the following.

First, a person is not entitled to a patent if the invention was "known or used by others in this country, or was patented or described in a printed publication in this or a foreign country" before the date of invention by the applicant for the patent. If, for example, an invention is known or is being used by someone in the United States, another person who makes the same invention at a later date may not obtain a patent. Prior knowledge or use in a different country, however, is not a bar to a patent application in the United States. In contrast, a prior patent or a printed publication anywhere in the world will bar an applicant for patent in the United States if it appeared before the date of the applicant's invention.

Second, a patent is barred if "the invention was patented or described in a printed publication in this or a foreign country or in public use or on sale in this country, more than one year prior to the date of the application for patent in the United States." This definition of prior art is similar to the first with one important distinction. In the first circumstance, the issue is whether the prior art was in existence before the date of invention. In the second circumstance, the issue is whether the prior art was in existence more than one year before the patent application was filed. There have been many cases in which an inventor has delayed in filing a patent application and has discovered, to his or her dismay, that the patent is barred because some other person put the invention into public use or described the invention in a printed publication after the patent applicant's invention but more than one year prior to the filing date of the patent application. This section also requires the inventor to file a patent application within one year of his or her publication, public use or marketing of an invention. Here too, if more than one year passes, a patent application is barred. Also in this section, a patent document or printed publication anywhere in the world is prior art, whereas public use or placing the invention on sale has an effect only if it occurs within the United States. The critical point is that if the event is more than one year before the filing date, the patent application is barred. There is no grace period. If a patent application is filed one year and one day after the critical event, the application is too late.

Third, an inventor is barred from obtaining a patent if he or she patents the invention outside of the United States before the date of the patent application in the United States, and if the application outside the United States was filed more than 12 months before filing the application in the United States. In other words, if an inventor files outside of the United States and then files in the United States within a 12-month period, any patent which issues on the non-U.S. application will not be prior art. However, if the inventor waits more than 12 months, the foreign patent will be prior art. The purpose of the rule is to require reasonable diligence in filing patent applications in different countries and to prevent a stringing out of the patenting process from one country to another.

There are several other bars to patentability that are important but are not, strictly speaking, prior art. Naturally, if an inventor abandons the invention, he or she cannot obtain a patent. Additionally, if A makes an invention, only A can apply for a patent on the invention.

Other specialized rules may prevent an inventor from obtaining a patent because of specific activities which stand as a prior art barrier.

In a fast-changing world, finding a single piece of prior art which discloses the same invention as that claimed in a patent is not the most likely scenario. What is far more likely to occur is that the prior art will be something similar but not identical to the patented invention. The patent statutes also provide for this situation—in a negative manner. Specifically, section 103 of the code provides that a patent may not be obtained "though the invention is not identically disclosed or described [in the prior art] if the differences between the subject matter sought to be patented and the prior art are such that the subject matter as a whole would have been obvious at the time the invention was made to a person having ordinary skill in the art." The test which is posed by this section is whether a worker of ordinary skill, knowing the prior art, would have found the patented invention obvious.

The rules for determining obviousness are difficult and perplexing for they call upon the courts and the parties to perform the very difficult task of imagining whether it would have been obvious to foresee an invention which is now known to everyone. In principle, obviousness is determined by comparing one or more pieces of prior art with the invention and then analyzing the points of similarity and difference.